Structure and method of making sealed capped chips

ABSTRACT

A method of making a plurality of sealed assemblies is provided which includes a) assembling a first element to a second element so that a bottom surface of the first element faces downwardly toward a front surface of the second element and a top surface of the first element faces upwardly away from the second element; and (b) forming ring seals surrounding regions of the front surface of the second element by introducing flowable material between the first element and the second element from the top surface of the first element through openings in the first element. A chip is provided which includes: (a) a body defining a front surface and one or more circuit elements on or within the body; (b) one or more bond pads exposed at the front surface in a bond pad region; and (c) a metallic ring exposed at the front surface, the ring substantially surrounding the bond pad region. Sealed chip assemblies are formed by sealing an array of the chips, e.g., in wafer form, to a cap element.

This application claims the benefit of the filing dates of U.S.Provisional Patent Application Nos. 60/506,500 filed Sep. 26, 2003,60/515,615 filed Oct. 29, 2003, 60/532,341 filed Dec. 23, 2003,60/568,041 filed May 4, 2004, 60/574,523 filed May 26, 2004, and is acontinuation-in-part of U.S. patent application Ser. No. 10/928,839,filed Aug. 27, 2004 entitled PACKAGE HAVING INTEGRAL LENS AND WAFERSCALE FABRICATION METHOD THEREFOR, on which Catherine De Villeneuve,Giles Humpston, and David B. Tuckerman are named inventors, thedisclosures of all such applications being hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to microelectronic packaging.Microelectronic chips typically are thin, flat bodies with oppositelyfacing, generally planar front and rear surfaces and with edgesextending between these surfaces. Chips generally have contacts on thefront surface, which are electrically connected to the circuits withinthe chip. Certain chips require a protective element, referred to hereinas a cap or lid, over all or part of the front surface. For example,chips referred to as surface acoustic wave or “SAW” chips incorporateacoustically-active regions on their front surfaces, which must beprotected from physical and chemical damage by a cap.Microelectromechanical or “MEMS” chips include microscopicelectromechanical devices, e.g., acoustic transducers such asmicrophones, which must be covered by a cap. The caps used for MEMS andSAW chips must be spaced from the front surface of the chip to an opengas-filled or vacuum void beneath the cap in the active area, so thatthe cap does not touch the acoustical or mechanical elements. Certainelectro-optical chips such as optical sensing chips and light-emittingchips have photosensitive elements which also must be protected by alid. Voltage controlled oscillators

Miniature SAW devices can be made in the form of a wafer formed from orincorporating an acoustically active material such as lithium niobate orlithium tantalate material. The wafer is treated to form a large numberof SAW devices, and typically also is provided with electricallyconductive contacts used to make electrical connections between the SAWdevice and other circuit elements. After such treatment, the wafer issevered to provide individual devices. SAW devices fabricated in waferform can be provided with caps while still in wafer form, prior tosevering. For example, as disclosed in U.S. Pat. No. 6,429,511 a coverwafer formed from a material such as silicon can be treated to form alarge number of hollow projections and then bonded to the top surface ofthe active material wafer, with the hollow projections facing toward theactive wafer. After bonding, the cover wafer is polished to remove thematerial of the cover wafer down to the projections. This leaves theprojections in place as caps on the active material wafer, and thusforms a composite wafer with the active region of each SAW devicecovered by a cap.

Such a composite wafer can be severed to form individual units. Theunits obtained by severing such a wafer can be mounted on a substratesuch as a chip carrier or circuit panel and electrically connected toconductors on the substrate by wire-bonding to the contacts on theactive wafer after mounting, but this requires that the caps have holesof a size sufficient to accommodate the wire bonding process. Thisincreases the area of the active wafer required to form each unit,requires additional operations and results in an assembly considerablylarger than the unit itself.

In another alternative disclosed by the '511 patent, terminals can beformed on the top surfaces of the caps and electrically connected to thecontacts on the active wafer prior to severance as, for example, bymetallic vias formed in the cover wafer prior to assembly. However,formation of terminals on the caps and vias for connecting the terminalsto the contacts on the active wafer requires a relatively complex seriesof steps. Similar problems occur in providing terminals for MEMSdevices. For these and other reasons, further improvements in processesand structures for packaging SAW, MEMS, electro-optical and other cappeddevices would be desirable.

SUMMARY OF THE INVENTION

As used herein in relation to a cap and cap wafer and a lid and lidwafer, the term “top surface” refers to an outer surface of the cap, andthe term “bottom surface” refers to an inner surface of the cap, theinner and outer surfaces of the cap relating to the form in which thecap is joined to the chip. Stated another way, the outer surface of thecap faces away from the front, i.e., the contact-bearing surface of thechip, while the inner surface of the cap faces towards the front orcontact-bearing surface of the chip. The outer surface of the cap isreferred to as the top surface, and the inner surface of the cap isreferred to as the bottom surface, even if the capped chip structureincluding both chip and cap is turned over and mounted, such that thetop surface faces downwardly and is joined to another article, such as aprinted circuit panel.

According to an aspect of the invention, a capped chip is provided whichincludes a chip having an upwardly facing front surface and a pluralityof bond pads exposed in a bond pad region at the front surface. A capmember having a top surface, a bottom surface opposite the top surface,and a plurality of through holes extending between the top and bottomsurfaces, is mounted to the chip such that the bottom surface faces thefront, surface of the chip and is spaced therefrom to define a void. Aplurality of solid electrically conductive interconnects extend from thebond pads at least partially through the through holes to form sealsextending across the through holes.

An assembly including a capped chip according to a preferred aspect ofthe invention further includes a circuit panel having a plurality ofterminals, wherein the interconnects are joined to the terminals of thecircuit panel.

According to a particular preferred aspect of the invention, theinterconnects may include a fusible conductive material joined to thebond pads. Wettable regions are desirably provided on sidewalls of thethrough holes, the fusible material contacting the wettable regions. Thefusible conductive material may include at least one of a solder, tin,or eutectic composition, and the through holes have a substantiallyfrusto-conical shape.

According to a particular preferred aspect of the invention, a sealdisposed between the bottom surface of the cap member and a portion ofthe front surface of the chip, the seal at least substantially enclosingthe bond pad region and the void. The chip preferably includes an activearea and the through holes are disposed between the seal and the activearea such that the seal and the interconnects seal the active areawithin the void. In one embodiment, the interconnects include a fusiblematerial and an attach temperature of a sealing material of the sealcoincides with a reflowing temperature for the fusible material.

In an embodiment, the bottom surface of the cap member includes a stop,the stop being engaged with the front surface of the active chip tocontrol a spacing between the cap member and the chip. A sealingmaterial of the seal is preferably disposed in contact with the stop andwith the front surface of the chip such that the cap member is sealed tothe chip at the stop. Illustratively, the stop includes a knife-edge andthe seal includes a material such as a thermoplastic, adhesive, lowmelting point glass, solder or eutectic composition. In one embodiment,the seal is diffusion bonded to at least one of the chip and the capmember.

In a particular embodiment, the seal includes spacing elements, suchthat the front surface of the chip and the bottom surface of the capmember are spaced by no less than a width of the spacing elements. Thecap member preferably includes at least one material selected from thegroup consisting of ceramics, metals, glasses, and semiconductormaterials. In a highly preferred embodiment, the cap member consistsessentially of a material having a coefficient of thermal expansion(CTE) closely matched to a CTE of the chip. Such chip may include asurface acoustic wave (SAW) device exposed at the front surface and thecap member includes a material having a CTE, which is closely matched toa CTE of the SAW device. In a specific embodiment, the SAW deviceincludes a component consisting essentially of lithium tantalate, andthe cap member includes a layer of aluminum and a layer of aluminumoxide overlying the layer of aluminum. In such embodiment, the capmember may include a metal layer and an oxide layer overlying the metallayer, the oxide layer including an oxide of a metal of the metal layer,wherein the oxide layer lines the through holes. The material of the capmember may further include one or more nickel alloys.

Preferably, through holes of the cap are metallized with two or morelayers of metal disposed on sidewalls thereof. The layers of metaldesirably include a layer consisting essentially of titanium contactingthe sidewall of the through hole, a layer consisting essentially ofplatinum contacting the titanium layer, and an exposed layer consistingessentially of gold contacting the platinum layer. Such metallization isa preferred example of a broader class of metallization schemescolloquially referred to as “under bump metallizations” (“UBMs”), a UBMtypically being applied to form a bondable surface on a larger surface,prior to applying a molten fusible conductive material thereto, such asa solder mass.

According to another preferred aspect of the invention, the chipincludes a rear surface opposite the front surface and peripheral edgesextending between the front and rear surfaces, and the cap memberincludes peripheral edges disposed between the bottom surface and thetop surface, wherein the chip further comprises an additional sealsealing at least the peripheral edges of the cap member to theperipheral edges of the chip.

According to yet another preferred aspect, the cap member includes adielectric layer having an inner surface and an outer surface, a groundlayer disposed on at least the inner outer surface and at least onetrace extending along the outer surface from the interconnect.

In a particular embodiment, the interconnects of the capped chip includestud bumps in conductive communication with the bond pads, and the studbumps extend at least partially through the through holes. Contacts atthe top surface of the cap member are disposed in conductivecommunication with the stud bumps.

In one embodiment, some of the stud bumps have shoulders abutting thebottom surface of the cap member, whereby the spacing between the bottomsurface and the cap member is determined by the shoulders.

In another particular embodiment of the invention, the through holes aretapered, becoming smaller in a direction from the top surface towardsthe bottom surface.

In a preferred embodiment, the interconnects include at least oneconductive trace extending horizontally along the top surface of the capmember. The interconnects may further include one or more contacts inconductive communication with the at least one conductive trace.

According to another aspect of the invention, a capped chip is providedwhich includes a chip having a front surface, and a plurality of bondpads exposed at the front surface. The cap member has a top surface, abottom surface opposite the top surface, and a plurality of throughholes which extend between the top and bottom surfaces. The cap memberis mounted to the chip such that the bottom surface faces the chip andis spaced therefrom to define a void. In such capped chip, a pluralityof electrically conductive interconnects extend from the bond pads atleast partially through the through holes. The interconnects including aflowable conductive material that extends at least partially through thethrough holes.

Preferably, the flowable conductive material extends from the bond padsthrough the holes. As in the above aspect of the invention, a sealpreferably extends between the chip and the cap member, the sealsurrounding at least some or all of the interconnects, and the flowableconductive material sealing the through holes. In one embodiment, theseal includes a flowable conductive material of the same composition asthe interconnects.

According to a preferred aspect of the invention, the flowableconductive material wets portions of the cap member surrounding thethrough holes. In a particular embodiment, the cap member defines wallsextending from the top surface to the bottom surface, the wallssurrounding each of the through holes and the flowable conductivematerial wets the walls. When the cap member includes a structuralmaterial not wettable by the flowable conductive material, the cap mayinclude liners formed from a material wettable by the flowableconductive material covering the walls. In a preferred embodiment, theflowable conductive material is a solder.

According to yet another aspect of the invention, a method of formingcapped chips is provided which includes assembling a lid member to achip member so that a bottom surface of the lid member faces downwardlytoward a front surface of the chip member and a top surface of the lidmember faces upwardly away from the chip member. Through-holes extendingbetween the top and bottom surfaces of the lid member are aligned withelectrically conductive features of the chip, member and so that thebottom surface of the lid member is spaced apart from the front surfaceof the chip member in at least some regions including the alignedthrough holes and conductive features. Electrical connections are formedwhich extend from the conductive features at least partially through thethrough holes. This is performed by providing a flowable conductivematerial at the through holes and causing the flowable conductivematerial to flow in the through holes.

According to particular aspect of the invention, the step of providing aflowable conductive material includes introducing the flowableconductive material into the through holes from the top surface of thelid member. The step of causing the flowable conductive material to flowmay include causing the flowable conductive material to flow downwardlyin the through holes into contact with the electrically conductivefeatures of the chip member. The electrically conductive featuresinclude features projecting upwardly from the front surface of the chipmember into the through holes. The electrically conductive features canbe spaced, for example, below the bottom surface of the lid member andthe step of causing the flowable conductive material to flow includesforming menisci projecting downwardly from the bottom surfaces at thethrough holes so that the menisci contact the conductive features. Inone embodiment, the step of causing the flowable material to flowincludes causing the flowable material to wet walls bounding the throughholes.

According to another aspect of the invention, a method of forming acapped chip having a plurality of metallic interconnects at leastpartially extending through a cap member is provided which includesaligning (i) a chip having a front surface, and a plurality of bond padsexposed at the front surface; with (ii) a cap member having ahorizontally extending top surface, a horizontally extending bottomsurface, and a plurality of through holes extending between the topsurface and the bottom surface, so that the through holes are aligned tothe bond pads. The method further includes forming solder-wettablemetallizations are formed on the cap member at least where the throughholes meet the top surface and simultaneously forming solder-wettablemetallizations overlying the bond pads of the chip, the solder-wettablemetallizations overlying the bond pads being formed in the self-alignedmanner to the through holes. The solder-wettable metallizations of thethrough holes are bonded to the solder-wettable metallizations on thechip to form metallic interconnects extending from the bond pads atleast partially through the through holes.

Preferably, the solder-wettable metallizations are formed by deposition,the aligned cap member functioning as an in situ mask during thedeposition of the solder-wettable metallizations on the chip.Specifically, the chip may include a surface acoustic wave (SAW) device,wherein the bond pads are not wettable by solder prior to thesolder-wettable metallizations being formed, e.g., such as when the bondpads of the chip have at least a surface film of aluminum. In oneembodiment, the bonding step includes disposing solder balls on thesolder-wettable metallizations of the cap, member and heating thealigned cap member and the chip to cause solder of the solder balls tobond the solder-wettable metallizations of the cap member to thesolder-wettable metallizations of the chip. In a particular embodiment,the bonding step is performed fluxlessly, i.e., without using a flux,such as may be performed in a nitrogen atmosphere.

According to an aspect of the invention, a method of making a chipassembly includes the steps of assembling (i) a capped chip including achip, a cap overlying a front surface of the chip and a sacrificiallayer overlying the cap with (ii) one or more further components. Afterthe assembling step, the sacrificial layer is removed from the cappedchip. Preferably, the assembling step includes bondingelectrically-conductive features of the capped chip to at least one ofthe further components using an electrically-conductive bondingmaterial.

Preferably, the electrically-conductive features of the capped chipinclude interconnections extending through the lid element. When that isthe case, the method preferably further includes the steps of patterningthe sacrificial layer and forming at least portions of theinterconnections using the patterned sacrificial layer as a mask.

In another preferred embodiment, the method further includes a step offorming the capped chip by assembling a lid member and a chip memberincluding a plurality of chips and then severing the lid member and chipmember, the sacrificial layer being present on the cap member during thesevering step.

According to another preferred aspect of the invention, a method isprovided for making a plurality of capped chip assemblies. The methodincludes the steps of: (a) assembling a lid member and a chip memberincluding a plurality of chips to one another so that the lid memberoverlies the chip member and a top surface of the lid member faces awayfrom the chip member; (b) severing the lid member and chip member toform a plurality of individual units each including one or more of thechips and a portion of the lid member; (c) providing a sacrificial layeroverlying the top surface of the lid member prior to the severing step;and (d) removing the sacrificial layer after the severing step.

In a preferred aspect of the invention, the cap includes a region whichis at least partially optically transmissive. The sacrificial layerdesirably includes a developed photoresist layer. The chip preferablyincludes at least one first bonding area, and the cap includes at leastone second bonding area including a wettable region. Preferably, in suchcase, the assembling step includes bonding, the first bonding area ofthe chip member to the second bonding area of the cap by a fusiblematerial.

According to another aspect of the invention, a capped chip is providedwhich includes a chip having a front surface and a plurality of bondpads exposed at the front surface. A cap member having a bottom surfacefaces the front surface of the chip and has a top surface opposite thefront surface. The cap member further has a plurality of through holesextending from the bottom surface to the top surface. In this aspect ofthe invention, at least portions of the through holes are tapered,becoming smaller in a direction from the bottom surface toward the topsurface. A plurality of electrically conductive interconnects extendfrom the bond pads at least partially through the through holes.

According, to a preferred aspect of the invention, the interconnectsinclude fusible material joined to the bond pads. The fusible materialmay includes solder, tin and/or a eutectic composition, for example, orsuch other suitable fusible material. In a preferred embodiment, thethrough holes have substantially frusto-conical shapes. A sealingmaterial is desirably disposed between the bottom surface of the capmember and a portion of the front surface of the chip. Preferably, anattach temperature of the sealing material coincides with a temperaturefor bonding the fusible material.

In one preferred aspect of the invention, a bottom surface of the capmember includes a downwardly protruding feature such as a knife edge.The sealing material is preferably disposed in contact with theprotruding feature and with the front surface of the chip to seal thecap member to the chip. In particular embodiments, the sealing materialincludes a thermoplastic, an adhesive, a low melting point glass, asolder, and a eutectic composition. In a preferred embodiment, thesealing material is diffusion bonded to at least one of the chip and thecap member.

Preferably, the sealing material includes spacing elements, such thatthe front surface of the chip and the cap member are spaced by no lessthan a width of the spacing elements. In one embodiment, the bond padsare exposed at a bond pad region of the front surface, and the cappedchip further includes a sealing material sealing the front surface, tothe bottom surface of the cap member, such that the sealing material atleast substantially encloses the bond pad region.

In a particular embodiment, the cap member consists essentially of atleast one material selected from the group consisting of ceramics,metals, glasses, and semiconductor materials. Preferably, the throughholes of the cap are lined with two or more layers of metal disposed onthe sidewalls. The layers of metal include, for example, a layerconsisting essentially of titanium contacting the sidewalls of thethrough holes, a layer consisting essentially of platinum contacting thetitanium layer, and an exposed layer consisting essentially of goldcontacting the platinum layer.

In one embodiment, the chip has a rear surface opposite the frontsurface and peripheral edges extending between the front and rearsurfaces. The cap member has peripheral edges disposed between thebottom surface and the top surface. In such embodiment, the chippreferably includes an additional seal sealing at least the peripheraledges of the cap member to the peripheral edges of the chip.

According to a particular aspect of the invention, an assembly isprovided which further includes a circuit panel having a plurality ofterminals, wherein the interconnects are joined to the terminals of thecircuit panel.

According to another aspect of the invention, a capped chip is providedwhich includes a chip having a front surface, a cap member having abottom surface facing the front surface of the chip and having a topsurface opposite the front surface. The cap member further includes aplurality of through holes extending from the bottom surface to the topsurface. A plurality of metallic interconnects including stud bumps areelectrically connected to the chip and project upwardly from the frontsurface at least partially through the through holes.

According to such preferred aspect, the chip has bond pads exposed atthe front surface and the stud bumps are joined to the bond pads andelectrically connected to the chip through the bond pads. The stud bumpspreferably extend at least to the top surface. The metallicinterconnects may include annular solderable metallizations whichsurround the through holes on the top surface of the cap member and thecapped chip preferably includes solder masses joining the solderablemetallizations to the stud bumps.

In a preferred embodiment, the stud bumps are sealed to the cap member.

In one embodiment, the through holes do not have solderablemetallizations. In such case, in a particular embodiment, the stud bumpsmay be sealed by a conductive organic material. For instance, the studbumps may be sealed by a nonconductive material and the stud bumpsprotrude through the nonconductive material, which is preferably anorganic material. In a highly preferred aspect of such embodiment,masses of an electrically conductive bonding material can be joined tothe stud bumps at positions external to the top surface.

In a particular embodiment, an assembly is provided including a cappedchip and further including an interconnection element. Theinterconnection element includes pressure contacts pressed against thestud bumps to electrically interconnect the interconnection element tothe capped chip.

In a particular embodiment, the metallic interconnects are coplanar withthe top surface.

In one embodiment, the stud bumps are sealed to the through holes of thecapped chip by the nonconductive material. The sidewalls of the throughholes may be oriented at an angle of about 90 degrees to the topsurface.

Alternatively, the through holes can be tapered, becoming smaller in adirection from the bottom surface towards a midpoint of a thickness ofthe cap member and becoming smaller in a direction from the top surfacetowards the midpoint of the thickness.

In other embodiments, the through holes are tapered and become smallerin a direction from the bottom surface towards the top surface; oralternatively, become smaller in a direction from the top surfacetowards the bottom surface.

Preferably, a sealing material is disposed between the bottom surface ofthe cap member and a portion of the front surface of the chip.

In one embodiment, an assembly is provided which includes a capped chipand further includes a circuit panel having a plurality of terminals,wherein the metallic interconnects are joined to the terminals of thecircuit panel.

In a particular embodiment, the stud bumps include at least one metalselected from the group consisting of aluminum, gold, silver, platinum,and copper.

According to another aspect of the invention, a method is provided ofmaking a capped chip assembly. Such method includes the steps of: (a)aligning a cap member with a chip member including one or more chips sothat electrically conductive elements projecting from a front surface ofthe chip member extend into through-holes in the lid member and at leastpartially control location of the lid member relative to the chip memberin one or more horizontal directions parallel to the front surface; and(b) forming interconnections extending through the lid member so thatthe interconnections include the conductive elements.

According to a particular aspect, the chip member includes contact padsand the electrically conductive elements include stud bumps projectingfrom the contact pads. The step of forming the stud bumps may beperformed by wire bonding to the contact pads before the aligning step.

In another preferred embodiment, the chip member includes contact padsand the electrically conductive elements include balls. In suchembodiment, the balls may be bonded to the contact pads before thealigning step.

In one embodiment, the electrically conductive elements hold the lidmember above the chip member during the forming step so that there is aspace between the lid member and the chip member at the conclusion ofthe forming step.

In a preferred embodiment, the chip member is a unitary wafer memberincluding a plurality of chips, and the method further includes severingthe lid member and the wafer member after the forming step so as toprovide a plurality of individual units, each unit including one or moreof the chips, a lid and one or more of the interconnections. In suchcase, the method may further include a step of forming a plurality ofring seals extending between the wafer member and the lid member so thateach the ring seal surrounds one or more of the interconnections. Inthat case, the severing step is performed so that each the unit includesone or more of the ring seals.

According to another aspect of the invention, a method is provided offorming a capped chip having a plurality of metallic interconnects atleast partially extending through a cap member, comprising: providing achip having a front surface and a plurality of bond pads on the frontsurface; providing conductive balls on the bond pads; providing a capmember having a horizontally extending bottom surface, a horizontallyextending top surface, and a plurality of metallized through holesextending from the bottom surface to the top surface; aligning the capmember and the chip such that the bottom surface faces the chip and themetallized through holes are aligned to the conductive balls; andbonding the conductive balls to the metallized through holes to form themetallic interconnects.

In a preferred embodiment, the conductive balls include a low meltingpoint material, such that the conductive balls are reflowed when theconductive balls are bonded to the metallized through holes.

In some embodiments, at least some of the through holes are tapered,having a dimension which becomes smaller from the bottom surface towardthe top surface. In one embodiment, the metallized through holespreferably have substantially frusto-conical shape and the conductiveballs have substantially spherical faces, such that the aligningself-locates the substantially metallized through holes onto thesubstantially spherical faces of the conductive balls.

Preferably, the aligning self-locates the metallized through holes ontothe conductive balls for variations in position having six degrees offreedom including first and second horizontal axes, a vertical axis, androtation, pitch, and roll.

In a preferred embodiment, the method further includes sealing thebottom surface of the cap member to the front surface of the chip.Preferably, such sealing is performed simultaneously with the reflowing.In a preferred aspect, the sealing includes depositing a sealingmaterial onto at least one of the bottom surface of the cap member andthe front surface of the chip, wherein the reflowing draws the capmember and the chip toward each other to complete the sealing.Preferably, an attach temperature of the sealing material coincides witha reflowing temperature of the conductive balls.

In one embodiment, the sealing is performed after the step of bonding.

In a preferred embodiment, the bottom surface of the cap member includesa downwardly protruding feature such as a knife edge, wherein a sealingmaterial is disposed in contact with the feature and with the frontsurface of the chip to seal the cap member to the chip. In such case, asealing material is preferably disposed in contact with the feature andwith the front surface of the chip to seal the cap member to the chip.

In another preferred aspect of the invention, the conductive balls areplaced on the bond pads in a fluxless manner, and the method furthercomprises joining the conductive balls to the bond pads prior to thestep of bonding the conductive balls. In such case, the conductive ballspreferably include solder balls.

In a preferred aspect, the chip includes a rear surface opposite thefront surface and peripheral edges extending between the front and rearsurfaces, and the cap member includes a top surface opposite the bottomsurface and peripheral edges disposed between the bottom and topsurfaces, the method further comprising depositing an additional sealingmaterial onto the peripheral edges of the cap member and onto thesealing material.

In a preferred embodiment, the above method used for forming a cappedchip can be further augmented include steps of aligning and joining themetallic interconnects to terminals disposed on a circuit panel to forman assembly.

According to another aspect of the invention, a method is provided offorming a plurality of capped chips each having a plurality of chipinterconnections at least partially extending through a cap member ofthe capped chip. Such method includes:

-   providing an array of chips each having a front surface and a    plurality of bond pads on the front surface, and providing    conductive balls on the bond pads. A cap member is provided which    includes a horizontally extending bottom surface, a horizontally    extending top surface, and a plurality of metallized through holes    extending from the bottom surface to the top surface. At least some    of the through holes are tapered, becoming smaller in a direction    from the bottom surface towards the top surface. The cap member and    the array of chips are aligned such that the bottom surface faces    the front surfaces of the chips and the metallized through holes are    aligned to the conductive balls. The cap member is joined to the    chips by bonding the conductive balls to the metallized through    holes, wherein the bonded conductive balls form at least part of the    chip interconnections.

In a preferred embodiment, the conductive balls include a low meltingpoint material, and the bonding is performed by reflowing the conductiveballs. Preferably, each of the chips of the array of chips is attachedto at least one other of the chips, and the method further includessevering the joined chips.

According to another aspect of the invention, a capped chip is providedwhich includes: a chip having a front surface and a plurality of bondpads exposed at the front surface; a cap member having a bottom surfacefacing the front surface of the chip and having a top surface oppositethe front surface, the cap member further having a plurality of throughholes extending from the bottom surface to the top surface; and aplurality of metallic interconnects extending from the bond pads atleast partially through the through holes, the metallic interconnectsincluding stud bumps joined to the bond pads, the stud bumps contactingand engaging at least one of (i) the top surface of the cap membersurrounding the through holes and (ii) inner surfaces of the throughholes.

According to such aspect, in one embodiment, the through holes of thecapped chip do not have solderable metallizations. In such case, thestud bumps are preferably sealed to the cap member, such as by aconductive organic material.

An assembly including a capped chip according to such aspect of theinvention may further include an interconnection element, in which theinterconnection element includes pressure contacts that are pressedagainst the stud bumps to electrically interconnect the interconnectionelement to the capped chip. Preferably, in such embodiment, the metallicinterconnects are coplanar with the top surface.

In a particular embodiment, the sidewalls of the through holes areoriented at an angle of about 90 degrees to the top surface.

An assembly including a capped chip according to such embodiment mayfurther include a circuit panel having a plurality of terminals, whereinthe metallic interconnects are joined to the terminals of the circuitpanel.

In a particular embodiment, the stud bumps consist essentially of atleast one metal selected from the group consisting of gold and copper.

According to yet another aspect of the invention, a method of making acapped chip is provided which includes the steps of:

-   (a) assembling at least one chip with at least one cap so that stud    bumps project from the chip at least partially through through-holes    in the cap; and (b) deforming the stud bumps into engagement with at    least one of (i) a top surface of the cap surrounding the    through-holes and (ii) walls of the through holes.

According to a preferred aspect, the deforming step is performed so thatthe stud bumps sealingly engage the through holes. In a preferredaspect, the method further includes a step of forming a metallurgicalbond between the stud bumps and a metallic layer on the top surface orthe walls.

According to yet another embodiment of the invention, a capped chip isprovided, which includes: a chip having a front surface, one or moredevices at the front surface, and a first annular solder-wettablemetallization enclosing the one or more devices. The capped chip furtherincludes a cap member having a top surface, a bottom surface oppositethe top surface, one or more through holes extending between the top andbottom surfaces and a second annular solder-wettable metallization atthe bottom surface in registration with the one or more through holesand the first annular solder-wettable metallization. A sealing mediumincluding a fusible material is bonded to the first and secondsolder-wettable metallizations.

According to a preferred aspect of the invention, the sealing mediumincludes at least one material selected from the group consisting ofsolder, eutectic composition, and tin.

In one embodiment, the one or more through holes is sized to permit aflow of the sealing medium from the through hole onto the first andsecond annular solder-wettable metallizations. In such case, the one ormore through holes is preferably tapered to become smaller in adirection from the top surface of the cap member towards the bottomsurface. In one embodiment, the chip may further include a plurality ofbond pads on the front surface enclosed by the first annularsolder-wettable metallization, and a plurality of metallic interconnectsextending from the bond pads at least partially through the cap member.

According to another aspect of the invention, a chip includes: (a) abody defining a front surface and one or more circuit elements on orwithin the body; (b) one or more bond pads exposed at the front surfacein a bond pad region; and (c) a metallic ring exposed at the frontsurface, the ring substantially surrounding the bond pad region. In apreferred aspect of the invention, a unitary wafer includes a pluralityof such chips.

According to yet another aspect of the invention, a method of making aplurality of sealed assemblies is provided. Such method includes: (a)assembling a first element to a second element so that a bottom surfaceof the first element faces downwardly toward a front surface of thesecond element and a top surface of the first element faces upwardlyaway from the second element; and (b) forming ring seals surroundingregions of the front surface of the second element by introducingflowable material between the first element and the second element fromthe top surface of the first element through openings in the firstelement.

According to yet another aspect of the invention, another method ofmaking a plurality of capped chips is provided. Such method includes:(a) assembling a lid member to a chip member so that a bottom surface ofthe lid member fades downwardly toward a front surface of the chipmember and a top surface of the lid member faces upwardly away from thechip member; and (b) forming ring seals surrounding regions of the frontsurface of the chip member by introducing flowable material between thelid member and the cap member from the top surface of the lid memberthrough openings in the lid member.

In a preferred aspect of such method, at least one of the bottom surfaceof the lid member and the front surface of the chip member has one ormore wettable regions forming at least a portion of one or more ringsand one or more non-wettable regions enclosed by the one or more rings,and the step of forming the ring seals includes contacting the flowablematerial with the wettable regions.

According to such aspect of the invention, preferably the bottom surfaceof the lid member and the front surface of the chip member have thewettable and non-wettable regions, and the assembling step is performedso as to at least partially align the wettable regions with one another.

The method preferably includes an additional step of formingelectrically conductive interconnections extending from the regions ofthe chip member surrounded by the ring seals through the lid member.

In a preferred embodiment, the flowable material is an electricallyconductive material and the step of forming conductive interconnectionsincludes forming the conductive interconnections using the sameelectrically conductive material.

-   In a particular preferred aspect, the method includes maintaining    the lid member spaced above the chip member at least in the regions    during the step of forming the ring seals.

According to another aspect of the invention, a packaged microelectronicdevice is provided, which includes: (a) a unit having a chip with anupwardly-facing front surface and a downwardly-facing rear surface, anda lid overlying at least a portion of the front surface of the chip, thelid having a top surface facing upwardly away from the chip and unitconnections exposed at the top surface of the lid. At least some of theunit connections are electrically connected to the chip. The devicefurther includes (b) a package structure including structure definingpackage terminals, of which at least some of the package terminals areelectrically connected to the chip, such that the package structure, theunit or both define a downwardly-facing bottom surface of the package,the terminals of the package structure being exposed at the bottomsurface.

According to a preferred aspect of the invention, the rear surface ofthe chip defines a bottom plane and the package terminals have exposedsurfaces disposed at, or below the bottom plane.

Preferably, in one embodiment, at least some of the package terminalsare disposed beneath the unit. In a particular embodiment, all of thepackage terminals are disposed beneath the unit.

According to a particular aspect, the unit connections have a unitconnection pitch and the package terminals have a package terminal pitchgreater than the unit connection pitch.

In a particular embodiment, the unit connections have a first layout inplan and the package terminals have a second layout in plan differentfrom the first layout.

In one embodiment, the unit includes vertical interconnect structuresextending from the chip to the unit connections, at least some of thepackage terminals being electrically connected to at least some of thevertical interconnect structures.

In a particular embodiment, at least some of the package terminals areelectrically connected to at least some of the unit connections.

In one embodiment, the package structure includes an interposerextending outwardly beyond the unit, and having a downwardly-facingbottom surface, the terminals being exposed at the bottom surface of theinterposer.

According to a particular preferred aspect, the device may furtherinclude traces on the interposer electrically connected to the unitconnections and the terminals.

In a particular embodiment, the device includes masses including anelectrically conductive bonding material, such as solder balls,connected to the terminals and projecting downwardly from the terminals.

According to one embodiment of the invention, the terminals of thedevice include posts projecting downwardly from the interposer.Preferably, such posts are integral with the traces.

In a preferred aspect of the invention, the structure includes a bottomdielectric element extending at or below the bottom plane, and thepackage terminals are carried on the bottom dielectric element.

In one embodiment, the structure further includes lead portionsconnected to the unit connections and extending downwardly from the unitconnections to the bottom dielectric element.

In a particular embodiment, the structure includes a dielectric elementhaving a bottom run extending at or below the bottom plane and having atleast some of the package terminals thereon. Such dielectric element hasa fold portion extending upwardly from the bottom run. Electricallyconductive traces are connected to at least some of the packageterminals and extend along the bottom run and the fold portion.

In one preferred aspect of the invention, the dielectric elementincludes a top run extending from the fold portion over the top face ofthe unit, and the traces extending along the top run.

In a particular embodiment of the invention, the package structureincludes a lead frame, and the lead frame includes leads which extend toor below the bottom plane and define the package terminals. In suchembodiment, the lead frame is preferably resiliently engaged with theunit.

In a particular embodiment, the package structure includes avertically-extensive spacer and one or more conductive vias extendingthrough the spacer. In such embodiment, the spacer can be such as todefine a cavity and the unit is disposed within the cavity. The spacerpreferably includes a plurality of dielectric layers superposed on oneanother, wherein the conductive vias extend through the dielectriclayers so as to form vertically-extensive interconnects extendingthrough the spacer.

An assembly including a packaged device according to a preferred aspectof the invention includes a mounting element having contact padsthereon, and an electrically conductive bonding material connecting thepackage terminals to the contact pads. In such assembly, at least one ofthe package structure and the bonding material provide mechanical,compliance between the contact pads and the unit.

According to another aspect of the invention, a microelectronic unit isprovided which includes: (a) a chip with an upwardly-facing frontsurface and a downwardly-facing rear surface. The chip has contactsexposed at the front surface and has bottom unit connections exposed atthe rear surface. The microelectronic unit further includes (b) a lidoverlying at least a portion of the front surface of the chip. The lidhas a top surface facing upwardly away from the chip and top unitconnections exposed at the top surface of the lid. At least some of thebottom unit connections of the chip are electrically connected to atleast some of the top unit connections.

According to a preferred aspect of the invention, the chip includesvertically-extensive conductive elements which extend through the chipand interconnect at least some of the bottom unit connections with atleast some of the contacts. The unit preferably further includesvertical interconnect structures which extend through the lid andconnect at least some of the contacts with at least some of the top unitconnections. In such manner, at least some of the bottom unitconnections are electrically connected to at least some of the top unitconnections by the conductive elements and the vertical interconnectstructures.

In one embodiment according to this aspect of the invention, the chipand the lid each define vertically-extensive edges, and the unitincludes traces which extend along at least one of the edges. At leastsome of the top and bottom unit connections are interconnected with oneanother by the traces.

In a particular embodiment, at least some of the traces include traceportions which extend between the chip and the lid. Preferably, the lidis sealed to the chip.

In one embodiment, at least a part of the bottom surface of the lid isspaced from the front surface of the chip so that the lid and the chipcooperatively define an interior space within the unit. In such case,the chip preferably includes one or more elements selected from thegroup consisting of microelectromechanical elements, acoustically activeelements and optoelectronic elements.

According to another aspect of the invention, a microelectronic chip isprovided which has front and rear surfaces, and an active elementselected from the group consisting of microelectromechanical elements,electroacoustical elements and optoelectronic elements. In such aspect,the active element is exposed at the front surface, and bottom contactsare exposed at the rear surface.

A particular microelectronic unit according to a preferred aspect of theinvention includes a chip and a lid covering the active element.

According to a particular preferred aspect of the invention, an assemblyis provided which includes a microelectronic unit and a circuit panelhaving contact pads thereon, the unit being mounted on the circuit panelwith the front surface facing upwardly away from the circuit panel andwith the bottom contacts electrically connected to the contact pads.

According to yet another aspect of the invention, a microelectronic unitis provided, which includes (a) a chip having an upwardly-facing frontsurface, a downwardly-facing rear surface and one or more edgesextending between the front and rear surfaces. Such chip furtherincludes (b) a lid overlying at least a portion of the front surface ofthe chip, the lid having a top surface facing upwardly away from thechip, a bottom surface facing toward the chip and edges extendingbetween the top and bottom surfaces. The unit also includes (c) edgeunit connections exposed at one or more of the edges.

The microelectronic unit preferably includes vertical interconnectstructures which are electrically connected to the chip and extendupwardly through the lid, of which at least some of the verticalinterconnect structures are exposed at the one or more of the edges ofthe lid so that the exposed vertical interconnect structures define theedge unit connections.

In a preferred embodiment, the lid is sealed to the chip.

In one embodiment, at least a part of the bottom surface of the lid isspaced from the front surface of the chip so that the lid and the chipcooperatively define an interior space within the unit. In such case,the chip may include one or more elements selected from the groupconsisting of microelectromechanical elements, acoustically activeelements and optoelectronic elements.

According to another aspect of the invention, a method is provided formaking a microelectronic unit. Such method includes: (a) assembling alid element with a wafer element including a plurality of chips so thata bottom surface of the lid element faces toward a front surface of thewafer element bearing contacts electrically connected to the chips. Suchmethod further includes (b) providing vertical interconnect structuresextending from the contacts upwardly through the lid element; and (c)severing the lid element and the wafer element along lines of severanceso as to form individual units. At least some of the lines of severanceextend through at least some of the vertical interconnect structures sothat the at least some of the vertical interconnect structures areexposed at edges of at least some of the units.

According to yet another aspect of the invention, a method is providedfor making a microelectronic unit. Such method includes: assembling alid element with a wafer element including a plurality of chips so thata bottom surface of the lid element faces toward a front surface of thewafer element bearing contacts electrically connected to the chips.Vertical interconnect structures are provided which extend from thecontacts upwardly through the lid element. Vertically-extensive vias areprovided which extend at least partially through the lid element.Electrically conductive material in the vias is electrically connectedto the vertical interconnect structures. Such method further includessevering the lid element and the wafer element along lines of severanceso as to form individual units, wherein at least some of the lines ofseverance extend through at least some of the vias so that theconductive material in at least some of the vias is exposed at edges ofat least some of the units.

According to another aspect of the invention, a method of making sealedmicroelectronic units is provided which includes providing a waferelement including a plurality of chips, wherein the chips of the waferelement includes device areas at the front surface. The method furtherincludes aligning a lid element to the wafer element so that a bottomsurface of the cap member faces toward a front surface of the waferelement. The lid element is bonded to the wafer element to provide alidded wafer element. The lidded wafer element is then partially severedalong lines of severance to at least partially define edges ofindividual microelectronic units. Thereafter, edges of themicroelectronic units are sealed with an impermeable medium. The liddedelement can thereafter be severed into the individual microelectronicunits.

According to a preferred aspect of the invention, the chips of the waferelement include bond pads at the front surface and the impermeablemedium is electrically conductive. In such aspect, the method furtherincludes forming metallic interconnects extending from the bond pads tothe top surface of the lid element. Lands are formed on the top surfacein conductive communication with the metallic interconnects, the landshaving at least portions including the impermeable medium, the portionsbeing formed when the edges are sealed.

According a highly preferred aspect of the invention, the lands arepreferably formed and the edges are sealed by forming a patternedphotoresist layer over the top surface and the partially defined edgesof the lidded wafer element. In such aspect, the impermeable medium isdeposited to overlie the lidded wafer element and to overlie thepatterned photoresist layer over the lidded wafer element. The patternedphotoresist layer is thereafter removed, such that the depositedimpermeable medium remains only where the impermeable medium does notoverlie the patterned photoresist layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3D are views illustrating a method of forming a capped chipaccording to an embodiment of the invention.

FIGS. 3E-3F are a sectional view and a plan view illustrating a cappedchip according to another embodiment of the invention.

FIGS. 3G-3H are sectional views illustrating a method of forming acapped chip according to the embodiment shown in FIGS. 3E-3F.

FIGS. 3I-3N are sectional views illustrating a method of forming cappedchip according to a variation of the embodiment shown in FIGS. 3G-3H.

FIGS. 3O-3R are sectional views illustrating capped chips according tostill other embodiments of the invention.

FIGS. 3S-3V are views illustrating a method of severing capped chipsaccording to another embodiment of the invention.

FIGS. 4A and 4B are a sectional view and a plan view correspondingthereto, illustrating a particular embodiment of the invention in whicha redistribution wiring trace is provided.

FIGS. 4C and 4D are views illustrating a capped chip on whichredistribution traces are provided on an underside of the cap, accordingto an embodiment of the invention.

FIG. 4E is a plan view illustrating a layout of a chip having bond padsdisposed along both vertical and horizontal edges of the chip.

FIG. 4F is a plan view illustrating a layout of a chip which isadvantageously packaged according to an embodiment of the invention, thechip having bond pads disposed along only vertical edges or onlyhorizontal edges.

FIG. 5 is a sectional view illustrating a particular embodiment in whicha bonding layer of a chip is formed through a cap, after mounting thecap to the chip.

FIGS. 6A-6B are sectional views illustrating a method of forming cappedchips having electrical interconnects which include stud bumps.

FIGS. 7A-7B are a sectional view and a plan view, respectively,illustrating an embodiment of a capped chip having redistribution wiringtraces on the cap.

FIGS. 7C-7E are sectional views illustrating embodiments of theinvention in which conductive interconnects are provided in form ofwire-bonds.

FIGS. 8A-11B are sectional views illustrating various methods ofmounting a unit including a capped chip to a circuit panel.

FIGS. 12-17 are sectional views illustrating stages in a method ofpatterning and using a sacrificial coating on a cap element to provide acapped chip.

FIGS. 18-23 are sectional views illustrating stages in a method ofmaking capped chips in which conductive features of the chips assist inself-locating the cap element.

FIGS. 24-26 are sectional views illustrating a variation of theembodiment shown in FIGS. 18-23 in which the conductive features includeconductive spheres having solid cores.

FIGS. 27-32 are sectional views illustrating embodiments of capped chipsin which electrical interconnects are formed which include stud bumpsextending from the chip into through holes in the cap.

FIGS. 33 and 34A are plan views illustrating a plurality of chips, and acap, respectively, from which microelectronic units are fabricated,according to an embodiment of the invention.

FIG. 34B is a sectional view of microelectronic units fabricated fromthe chips and the cap illustrated in FIGS. 33-34A.

FIG. 35 is a plan view illustrating a plurality of caps of a cap elementfrom which microelectronic units are fabricated, according to oneembodiment of the invention.

FIGS. 36A-B are a plan view and a sectional view, respectively,illustrating a plurality of caps of a cap element from whichmicroelectronic units are fabricated, according to one embodiment of theinvention.

FIG. 37-43 are sectional views illustrating various embodiments ofmicroelectronic units having lidded or capped chips, and assembliesincluding such units, according to various embodiments of the invention.

FIGS. 44-49B are sectional views illustrating methods of fabricatingmicroelectronic units having lidded or capped chips, which have edgeconnections, and methods of mounting the units to circuit panels orother elements.

FIGS. 50-56 include sectional and elevational views illustrating variousembodiments of microelectronic units having bottom unit connections andmethods of making such units.

FIGS. 57-60 are sectional views illustrating stages in fabrication ofmicroelectronic units in which an impermeable medium is used to seal theunits.

FIG. 61 is a sectional view illustrating an alternative embodiment ofthat shown in FIG. 60, in which the impermeable medium is conductive andis patterned to form conductive traces.

DETAILED DESCRIPTION

FIGS. 1-3D illustrated a capped chip and stages in a method forfabricating a capped chip according to an embodiment of the invention.In particular, FIG. 3C is a sectional view illustrating a capped chip200 and FIG. 3D is a plan view illustrating the interconnects and theseal provided on the surface of a chip included in the capped chip.

Particular types of devices, such as SAW devices and MEMs need to besealed hermetically in order to function appropriately over the life ofthe device. For many silicon semiconductor devices, a package isconsidered to be hermitic if it has a leak rate of helium below 1×10⁻⁸Pa m³/sec. Other devices such as electro-optical devices do not requirehermeticity, but nevertheless are best packaged under a protective lid,e.g., one that is optically transmissive, as a way of preventingparticles from reaching a surface of the electro-optic device.

In a method of forming the capped chips, a plurality of caps 102, e.g.,as contained in a multiple cap-containing element 100 or wafer, aresimultaneously mounted to a plurality of chips, e.g., a wafer containingthe chips, and then the chips are severed to form units 300, as bestseen in FIG. 3C. In such method, as shown in FIG. 1, the cap element 100includes a plurality of caps 102, joined at boundaries 101. The capelement 100 can be either rigid or somewhat flexible, and a variety ofmaterials are available for its construction. In one embodiment, whenthe area of the cap element 100 and the chips to be joined are fairlylarge, the cap element 100 consists essentially of one or more materialsor a composition of materials which has a coefficient of thermalexpansion (hereinafter “CTE”) similar to that of the chips that are tobe capped. For example, the cap element 100 may include or consist ofone or more materials such as ceramics, metals, glasses andsemiconductor materials. When the chips are provided on a silicon waferor other such semiconductor wafer having a relatively low CTE, the capelement 100 can consist of a CTE-matched material such as silicon orother semiconductor, aluminum, nickel alloys, including those havingespecially low CTEs such as alloys of nickel and iron and alloys ofnickel and cobalt. Other CTE-matched metals include molybdenum.

When the device region 208 includes a SAW device, the cap element isdesirably constructed of a material having a CTE which is matched tothat of the SAW device, When such SAW devices are fabricated in lithiumtantalate wafers, a preferred choice for the cap element is aluminum,because aluminum has a CTE which is similar to that of SAW devices, anda low modulus of elasticity, and aluminum can be oxidized to formaluminum oxide, which is an insulator, by processes such as “anodizing”.In such manner, insulating layers are formed on the top surface, bottomsurface, and through holes with which to isolate respective ones of thesubsequently formed electrical interconnects from each other.

As further shown in FIG. 1, the cap element 100 and each cap 102 thereofhas a top surface 105 and a bottom surface 103. In one embodiment asshown, the top and bottom surfaces define respective planes. Throughholes 104 are provided in the cap element 100, the cap element 100generally having one or more through holes per chip. Through holes areprovided by any technique suited for the particular material ormaterials of which the cap element is made. For example, when the capelement 100 is composed predominantly of silicon, metal, ceramics andglasses, the through holes can be provided by a subtractive process suchas etching or drilling. Alternatively, when the cap element 100 includesa polymer, the through holes are more desirably provided through amolding process. In the embodiment shown in FIG. 1, the cap element 100consists predominantly of a dielectric or semiconductor material such asa glass, ceramic or a silicon wafer. Typical etching methods applied towafers of such materials result in through holes which are tapered asshown to grow smaller from one surface towards the other surface, suchthat they have a substantially frusto-conical shape. In this embodimentshown in FIG. 1, the through holes are tapered to become smaller in adirection from the top surface towards the bottom surface. In theembodiment shown in FIG. 1, bonding layers, e.g., regions 106 which arewettable, illustratively, by a fusible medium such as solder, tin, or aeutectic composition, are provided on the sidewalls 107 of the throughholes 104. The tapered profile of the through holes generally assists inpermitting the wettable regions to be formed on the sidewalls 107 of thethrough holes 104 by deposition. Suitable bonding layers will vary withthe material of the cap element and the fusible material which is usedto form the bond. The particular fusible medium may affect the impedancecharacteristics of the bond that is formed. For use with a fusiblemedium such as a low-melting point tin-based solder and a semiconductor,ceramic or glass cap element 100, one exemplary bonding layer includes a0.1 μm thick layer of titanium overlying the sidewalls of the throughholes 104, an additional 0.1 μm thick layer of platinum overlying thetitanium layer, and a 0.1 μm thick exposed layer of gold overlying theplatinum layer.

As shown in FIG. 2A, the cap element 100 is aligned to a plurality ofattached chips 202, such as contained in a wafer 201 or portion of awafer and is sealed to the water by a sealing medium 206. The sealingmedium 206 includes, illustratively, an adhesive, a glass, especiallythose which have a low-melting point, a fusible material such as solder,or another material which forms a diffusion bond to elements, e.g., thesealing medium may be such as to form a bond to a bonding ring, as willbe shown and described below with reference to FIGS. 33-36B. The sealingmaterial preferably includes a material such as any one or more of thefollowing: a thermoplastic, an adhesive, and a low melting point glass,which typically will bond the bottom surface 502 of the cap directly tothe front surface 601 of the chip, without requiring interveningmetallizations. Otherwise, bonding may be performed by solder, eutecticcomposition or one or more metals capable of forming a diffusion bondwith a metallization provided on the front surface 601 of the chip,e.g., a sealing ring 802, and a corresponding metallization 804 providedtherefor on the bottom surface of the cap 500. When the sealing materialhas an attach temperature that is coincident with the solder flowtemperature, the seal forms as the abutting bottom surface of the capand the front surface of the chip are drawn together by the decreasingheight of the solder.

The wafer 201 is also shown in plan view in FIG. 2B. Illustratively, thewafer is one of many available types of wafers which include at least alayer of semiconductor material, including but not limited to silicon,alloys of silicon, other group IV semiconductors, III-V semiconductorsand II-VI semiconductors. Each chip 202 includes a semiconductor deviceregion 204 provided in the semiconductor device layer, which contains,for example, one or more active or passive devices formed integrally tothe semiconductor material of the chip. Examples of such device include,but are not limited to a microelectronic or micro-electromechanicaldevice such as a SAW device, MEMS device, VCO, etc., and anelectro-optic device. When such device is present, the bottom surface103 is spaced from the front surface 216 of the chip 202 so as to definea gas-filled void or vacuum void 214 between the cap element 100 and thechip 202. The device region 204 of each chip 202 is conductivelyconnected by wiring 210 to bond pads 208 disposed in a bond pad regionat the front surface 216 of each chip. In some types of chips, the bondpads 208 include solder-wettable regions which are exposed at the frontsurface. In one embodiment, the device region 204 includes a SAW device,and the sealing medium is disposed in an annular or ring-like pattern ina way that surrounds the bond pads 208 and the device region 204 tohermetically seal each cap 102 to each chip 202.

FIGS. 3A-3C are further sectional views illustrating further stages inwhich electrically conductive interconnects 303 are formed which extendfrom the bond pads 208 of each chip 202 into through holes 104. As shownin FIG. 3A, a mass, e.g. a ball of a flowable conductive medium 302 isprovided at the through hole 104 at the top surface 105 of the capelement 100. Illustratively, the ball 302 includes a fusible conductivematerial such as, solder, tin or a eutectic composition. The mass offusible material 302 may be placed on the cap element 100 so as to restsomewhat inside the through hole 104, as shown. When the fusiblematerial 302 is a solder ball or ball of other fusible material, theballs can be placed at or in the through holes of the cap element byplacing and aligning a screen containing holes over the cap element andallowing the balls to drop through the holes of the screen into thethrough holes 104 until one such ball rests in each through hole inwhich a conductive interconnect is to be formed. Thereafter, as shown inFIG. 3B, the fusible material of the balls is caused to form bonds tothe bond pads 208 of the chips 202 of the wafer. For example, when theconductive material is a fusible material such as solder, tin oreutectic composition, heat is applied to the balls directly or byheating the cap element and the chip to a point that causes the materialto flow. As a result of this process, the fusible material flows ontoand wets the metallizations 106, and flows onto and wets the bond pads208 to form a bond to the bond pads 208 of the chip 202. Another resultof this process is that the fusible conductive material 304 forms aunified solid electrically conductive interconnect 303 which extendsfrom the bond pad 208 into the through hole to form a solid mass of thefusible conductive material. The thus formed conductive mass extendsacross the full width of the through hole to seal the through hole andto thereby separate the void 214 underlying the cap from the ambientmedium which is present above the through hole.

Thereafter, the assembly formed by the cap element 100 and the wafer 201is severed at dicing lanes defining their boundaries 101 into individualcapped chips, one of which is shown in FIG. 3C.

The plan view of FIG. 3D illustrates features on the surface of the chip202 as completed, the features including the device area 204 of the chip202, the interconnects 303 which are joined to bond pads of the chip,and the seal 206 which is disposed as an annular or “ring” structuresurrounding the bond pads and the device area 204.

Note, with respect to the above processing, that various stages ofprocessing can optionally be performed in different facilities, as therequired cleanroom level, i.e., a level specifying the maximumconcentration of contaminating particles in the air and on surfaces ofthe facility, varies during the stages of processing. Moreover, some ofthe stages of processing are best performed in facilities which areoriented to performing certain steps of processing. In addition, in apreferred embodiment, testing is performed as to intermediate results ofprocessing to eliminate product and materials from the process streamwhich are determined to be defective at particular stages of processing.

Thus, with respect to the processes described in the foregoing, afacility can fabricate cap elements, e.g. cap wafers having dimensionssized to fit the chip-containing wafers to be covered thereby. As anexample, such cap elements are fabricated from blank wafers, which canbe either new or possibly wafers recycled from previous processing. Thecap elements are subjected to processing to form the through holes,which are then tested to assure conformance to standards of quality,e.g., placement, location, alignment, pitch, depth, sidewall angle,etc., and any of several other criteria for assuring quality. In eitherthe same or in another facility, when the through holes include wettableregions, e.g., under bump metallizations (“UBM”) on the sidewallsthereof, processing is then performed to form the wettable regions.Because of the techniques used, and the increased sizes of features ofthe cap element, and tolerances therefor, these particular steps can beperformed in facilities which need not be geared to the fabrication ofsemiconductor devices. However, such steps can be performed in asemiconductor fabrication facility, if such is desired. Again, at theconclusion of this processing, testing is optionally performed to assurethat the wettable regions of the cap element meet quality standards.

Thereafter, the cap element and the chip-containing wafer are joinedtogether according to processing such as described above with referenceto FIG. 2A, such joining process preferably being performed in afacility having a high cleanroom level. For example, such process isdesirably performed in a semiconductor fabrication facility, such as thefacility in which the chip wafer is made. When the chips includeoptically active elements such as imaging sensors, processing tocomplete the conductive interconnects 303 (FIG. 3B) of each cap elementcan be deferred until later processing, if desired, since the primaryconcern is to mount the cap element as a cover over the chip wafer toavoid dust contamination. However, if the chip contains a SAW device,MEMs device or other such device requiring hermetic packaging, it isdesirable to form the conductive interconnects 303 at this time as well,to form a seal which protects the SAW device during subsequent stages ofprocessing. Again, some testing is then desirably performed to assurethat quality standards are met prior to proceeding to subsequent stagesof fabrication. Subsequent processing to form the electricalinterconnects, if not formed already, and to provide any, furthersealing, if necessary, is then performed. Such processing can beperformed in another facility other than the semiconductor fabricationfacility, and at a cleanroom level that is not required to be as high asthat of a semiconductor fabrication facility.

Similarly, subsequent processing to complete the packaging, as by addingother elements, e.g., optical lenses, interposer elements, thermallyconductive elements and the like, and processing to mount the packagedchip to a circuit panel, such as the processes described below withreference to FIGS. 7C-11B, or FIGS. 16-17, for example, need not beperformed in the same facility. Such subsequent processing can beperformed in environments which do not have the same cleanroom level asthat in which the cap element is mounted to the chip-containing wafer,that step preferably being performed in the semiconductor fabricationfacility.

The mounting of a cap element to a chip wafer, as described in theforegoing, is especially advantageous for the packaging of certain typesof chips, especially those including SAW devices, MEMs devices, andoptical devices, potentially resulting in increased yields, due to theability of such processing to be performed efficiently in cleanroomenvironments of semiconductor fabrication facilities, where sources ofcontamination are kept to a minimum. In particular, it is especiallydesirable to protect chips which include imaging sensors such ascharge-coupled device (CCD) arrays and the like from dust or otherparticle contamination by attaching a cap or lid to the front surface ofthe chip, as early in the packaging process as possible. Such imagingsensors include an imaging device array of a chip, over which a layerincluding an array of bubble-shaped microlenses is formed in contactwith the device array. The array of microlenses typically includes onemicrolens per pixel unit of the device array, the pixel unit havingdimensions of a few microns on each side. In addition, such microlensesare often made of a sticky material to which dust tends to adhere aftermanufacture. Particles and dust, if allowed to settle directly on animaging sensor, can obscure a portion of the pixel area of the imagingsensor, causing the image captured by the sensor to exhibit a black spotor degraded image.

However, owing to the shape of the microlenses and their number, and thesticky nature of the material used to make them, it is virtuallyimpossible to remove dust or other particles that settle on the surfaceof a typical imaging sensor having such microlenses. Thus, any particleswhich settle on the imaging sensor at any time after the microlens arrayis formed, such as during the packaging process, render the imagingsensor defective, such that it must be discarded. This provides anexplanation why such imaging sensor chips, when packaged according toconventional chip-on-board techniques, exhibit a yield rate in the finalpackaged chips, which is only 80% to 85% of the chips fabricated on eachwafer.

On the other hand, particles and dust which settle on a transparent capor cover above the outer surface of the chip do not obscure a portion ofthe image because the outer surface of the cap lies outside of the focalplane of the device. At worst, particles settling on the cover result inslightly decreased light intensity striking a portion of the imagingsensor. The slightly decreased light intensity rarely affects thequality of the image captured by the imaging sensor. Moreover, asdescribed herein, the caps or covers can be mounted over the imagingsensors of the chips while the chips remain attached in wafer form,i.e., before the wafer is diced into individual chips. The mounting ofthe caps is preferably performed in substantially the same level ofcleanroom environment as that used to fabricate the wafer, e.g., beforethe chip wafer leaves the semiconductor fabrication facility. In suchmanner, dust and particles are prevented from ever reaching the surfaceof imaging sensors of the chips. Moreover, once the chips are protectedby such transparent caps, it becomes possible to clean the top surfacesof the covers if particles such as dust reach them. This is because thetransparent caps can be made substantially planar, unlike the topographyof the bubble-shaped microlenses of the imaging sensor, and aretypically made of a material such as glass, which is readily cleaned bya solvent. Because the potential for direct dust contamination of theimaging sensor is virtually eliminated once the transparent cap wafer ismounted to the chip wafer, it is estimated that imaging sensor chipswhich are provided with transparent covers early in the packaging cyclehave a yield rate of 97%-99%. In such case, the defect rate becomes nolonger primarily due to contamination of the imaging sensors, butrather, for other reasons such as electrical functionality.

Desirably, wafer-level testing is performed on the chip-containing wafer201 (FIG. 3B) prior to the cap element 100 being joined to the wafer 201and the conductive interconnects 304 formed thereto. “Wafer-leveltesting” refers to such testing as is generally performed on chips,prior to the chips being severed into individual chips. More extensivetesting, commonly referred to as “chip-level testing,” is typicallyperformed only after the chip has been severed from the wafer andpackaged as an individual chip.

Wafer-level testing typically tests for basic functionality, such as forelectrical continuity, and basic functional operation of each chip. Suchtesting is desirably performed prior to individually packaging eachchip, in order to eliminate the costs of packaging chips that are laterdetermined to be defective. Thus, it is desirable to perform steps tocomplete the packaging of chips only with respect to chips which havepassed initial wafer-level testing; i.e., “known good dies.” Bycompleting the packaging only as to “known good dies,” unnecessarypackaging operations and/or rework of packaging operations are avoided.

Wafer-level testing generally takes much less time, perhaps as much as100 times smaller amount of time per chip tested than chip-leveltesting. However, the cost per chip of wafer-level testing performed byequipment capable of mechanically probing the surface of the wafer canequal or exceed that of the cost of chip-level testing, despite thegreater amount of time per chip needed, to perform chip-level testing.The special equipment required to precisely, mechanically probe thecontacts on the wafer surface is very expensive. For that reason, suchspecial equipment is typically also subject to resource constraintswithin the manufacturing facility. Moreover, fewer contacts per chipsare capable of being simultaneously contacted by such equipment than isgenerally the case for chip-level testing, for which chips are generallyplaced in sockets for testing. Another factor that affects the cost ofwafer-level testing is that the special equipment used to probe thecontacts of the wafer is limited to testing a single chip at a time, toat most a few chips at one time.

On the other hand, chips that are processed into capped chips in waferform or lidded chips in wafer form, as described herein, e.g., in FIGS.1-3D, are capable of being tested at the wafer level, with testequipment that is potentially less expensive than the mechanical probingequipment described above, because interconnects of the chips aredisposed on the top surface of the cap wafer and for that reason, arecapable of being probed by equipment similar to that used to performchip-level testing. For example, the top or outer surface of the capwafer can be mechanically contacted by a contact-bearing dielectricelement of test equipment, the contacts of the test equipment being heldin contact with the conductive interconnects of multiple chips of thewafer, as by mechanical force. In such manner, testing is performedthrough voltages and/or currents applied through the interconnects 303of each capped chip 300 to a plurality of the chips which remainattached in form of the wafer 201 (FIG. 3B). In that way, a plurality ofchips of each wafer are simultaneously tested and determined to be goodor defective, using equipment that can be less expensive than the,above-described test equipment, because the need to mechanically probethe wafer surface directly is eliminated. In a particular embodiment, agreater subset of tests than is generally performed as “wafer-leveltesting” is performed to the capped chips. This is possible because thewafer containing the capped chips is able to be tested by test equipmentthat is less expensive than the mechanical probing equipment discussedabove. In addition, the ability to test a greater number of the chips atone time permits more testing to, be performed per chip for the sametotal amount of test time using the less expensive test equipment. In ahighly preferred embodiment, the capped chips are tested in suchequipment for all or nearly all of the same functions ordinarilyperformed during chip-level testing, prior to the chips being severedfrom the capped chip-containing wafer into individual capped chips.

FIGS. 3E and 3F illustrate a variation of the above-describedembodiment, in which a sealing material is disposed between the chip 202and the cap 102 in such way that it separates electrical interconnects350 of the capped chip from adjacent electrical interconnects.

FIGS. 3E and 3F are a sectional view of such capped chip and a plan viewcorresponding thereto, through line 3F-3F. In this embodiment, thecapped chip 340 includes a sealing material 346 which surrounds thedevice area 204 of the chip 202, as in the above embodiment, but alsoencompasses the area of the electrical interconnects 250. Preferably,the sealing material is an insulating material, for example, anonconductive polymer, e.g., adhesive such as epoxy or other adhesive, athermoplastic, a glass, e.g., low-melting point glass, etc., such asdescribed above, such that the sealing material provides an isolatingmedium between adjacent ones of the electrical interconnects.

As further shown in FIG. 3E, optionally, a seal ring layer 342 isdisposed on the front surface of the chip 202, such that the sealingmaterial 346 adheres to the seal ring layer 342. The seal ring layerpresents a surface that is wettable by the sealing material 346 suchthat the sealing material preferentially wets the seal ring layer andforms a bond thereto. The capped chip optionally includes a guard ring348 which is used to prevent the sealing material from flowing beyondthe wettable seal ring layer towards the device area 204 of the chip202. The guard ring presents a surface which is not wettable by thesealing material. Certain materials present nonwettable surfaces toother materials. For example, polytetrafluoroethylene (PTFE) presents asurface to which most other materials will not adhere or wet. In oneembodiment, the guard ring 348 includes PTFE as a material at theexposed surface thereof. A similar seal ring layer and guard ring areoptionally provided on the facing surface 103 of the cap.

Herein, while processes and accompanying figures are generally describedin relation to individual chips and individual caps, unless otherwisenoted, they shall also be understood to apply to the simultaneousprocessing of multiple attached chips, e.g., a wafer, and multipleattached caps of a cap element, e.g., a cap wafer.

FIGS. 3G through 3H illustrate one option for fabricating the cappedchip shown in FIGS. 3E-3F. As in the above-described embodiment, thisembodiment is preferably practiced as a way of simultaneously mounting achip member including a plurality of chips to a cap member including aplurality of caps, after which the resulting joined article is severedto provide individual capped chips. As shown in FIG. 3G, the insulativesealing material 346 is placed on the surface of the chip 202 or the cap102. The cap, having pre-formed through holes therein, is thenjuxtaposed and aligned to the chip such that the sealing material 346contacts and wets respective areas of the cap 102 and the chip 202,including the seal ring layer 342, but not wetting the guard ring 348.As a result, the sealing material flows onto and is disposed on thecontacts, e.g., the bond pads 208 of the chip 202.

Thereafter, as shown in FIG. 3H, a process is performed to removeunwanted sealing material 346 which is disposed on the bond pads 208.Such process is preferably tailored to the specific sealing materialthat is used. For example, when the sealing material is a glass, theprocess is preferably performed by etching, which is preferablyperformed anisotropically, e.g., such as by reactive ion etching,sputter etching, or other process which includes removal of materialprimarily in the vertical direction. However, in another embodiment, theetching process need not be highly anisotropic. The etching process mayeven be a generally isotropic process, if the relative thickness 352 ofthe sealing material being removed is comparatively smaller than thedimensions 354 (FIG. 3F) between adjacent, ones of the bond pads 208. Inthat way, the removal of the sealing material 346 from on top of thebond pads 208 does not result in areas wide enough for adjacentelectrical interconnects to contact each other. In a particularembodiment when the sealing material is an organic material, e.g., apolymer such as an adhesive or thermoplastic, the removal is performedby a “plasma ashing” process, in which plasma etching results in thepolymer being converted to an ash-like substance, leaving the surfacesof the bond pads 208 exposed. Thereafter, the electrically conductiveinterconnects 350 are formed by a process such as one of theabove-described processes.

FIGS. 3I through 3N illustrate an alternative process for making cappedchips similar to those described above with reference to FIGS. 3Ethrough 3H. Referring to the completed capped chip as shown in FIG. 3N,this embodiment differs from the embodiment described therein, in thatthe sealing material 356 is a self-fluxing underfill. A self-fluxingunderfill is an insulative material that is frequently used to fill aspace between the front surface of a chip and a packaging element towhich it is mounted in a flip-chip arrangement. Typically, aself-fluxing underfill material is an epoxy-based material, which isviscous as applied at a normal ambient temperature, or at a slightlyelevated temperature, but which hardens into a solid mass upon heating.The self-fluxing aspect of the material relates to components of thecomposition which cause it to function as a flux when articles aresoldered in its presence. Stated another way, the self-fluxing underfillmaterial carries away reaction products, e.g., oxidation products fromthe soldering process that is performed in contact with it. In aparticular embodiment shown in FIG. 3N, the self-fluxing underfillmaterial is disposed in contact with a sealing ring layer 342 and isprevented from contacting the device area 204 of the chip by a guardring. The sealing ring layer is similar to the sealing ring layer andthe guard ring described above with reference to FIGS. 3E-3F. A Similarsealing ring layer (not shown) and guard ring (not shown) may also bedisposed on the underside 103 (bottom side) of the cap member 100.

A process of forming capped chips using such self-fluxing material willnow be described, with reference to FIGS. 3I through 3N. An initialstage in fabricating a capped chip is illustrated in FIG. 3I. In suchstage, a cap member 100 including a plurality of caps 102 is aligned toand disposed overlying a chip member 200 which includes a plurality ofattached chips 202. For example, the cap member 100 and the chip member200 can be held together in a fixture. Thereafter, as shown in FIG. 3K,the through vias of the cap are loaded with a fusible conductive medium,e.g. solder, tin, eutectic composition, or diffusion bondable medium,etc. In such case, the fusible conductive medium may adhere to the walls107 of the through holes, the walls preferably presenting surfaces whichare wettable by the fusible conductive medium. Alternatively, the wallsare metallized to, provide surfaces wettable by the fusible medium, asdescribed above. One method of applying the fusible medium shown in FIG.3J is by paste screening. Another method includes application of moltensolder to the cap 102 at the through hole, for example. The result ofthis step is to provide a solder mass held to the cap 102 at the throughhole 358, such as through a bond, adhesion, surface tension, etc. FIG.3K illustrates an alternative, in which the fusible medium is applied inform of a ball such as a solder ball 304, in a manner such as thatdescribed above with reference to FIG. 3A. Thereafter, the self-fluxingunderfill material is applied between the cap member 200 and the chipmember 100 to the space surrounding the device region 204 of each chip,resulting in the structure as shown in FIG. 3L and 3M. The self-fluxingunderfill material can be provided to the sealing surfaces at theperiphery of each chip of the chip member and each cap of the cap memberthrough capillary action. For example, referring again to FIG. 2B, thefilling process is conducted by applying the sealing material onto thesealing surfaces of the chips and the caps that are disposed alongrectilinear dicing channels, including the vertical dicing channels 211of a chip member such as a wafer, and also along horizontal dicingchannels 213.

In a particular embodiment, if the above-described capillary action isnot sufficient to achieve adequate fill quality, the process can beconducted as to a smaller number of attached chips and caps, for whichsuch filling method is adequate. For example, in an embodiment, the capmember contains a one-cap wide strip of chips and the chip membercontains a one-chip wide strip of chips. The underfill is applied to theinterface between peripheral edges of each chip and each cap on thestrip, and the self-fluxing material is then drawn onto the wettablesealing ring layers that are disposed adjacent to the peripheral edgesof each chip.

After the underfill is applied, the structure, as shown in either ofFIGS. 3L and 3M is heated, such that the fusible medium, e.g., solder,flows down the walls of the through holes to wet, contact and bond withthe bond pads 208 of the chips 202, as shown in FIG. 3N. During suchheating step, the self-fluxing underfill 356 is displaced by the moltenmedium. The self-fluxing underfill then preferably also provides flux tocarry away oxides which may occur due to the bonding process, such thata good conductive bond is achieved between the resulting electricalinterconnects 350, as provided by the fusible medium 358, and the bondpads 208. Thereafter, as in the embodiment described above withreference to FIGS. 1-3D, the structure is severed into individual cappedchips.

In a variation of the above embodiment, the self-fluxing underfillmaterial is provided to at least one of the opposing surfaces 103, 216of the chip member and the cap member prior to aligning and placing thecap member into a desired position relative to the chip member.

In another embodiment as shown in FIG. 30, masses of fusible conductivematerial are pre-bonded to wettable surfaces of the through holes 104 ofthe cap 102, and the cap is then bonded by a conductive adhesive 316provided on bond pads 208 of the chip 202, to form electricallyconductive interconnects extending from the bond pads 208 through thethrough holes to the top surface 105, of the cap 102. Again, thisprocess is preferably performed simultaneously as to a plurality ofattached chips, such as a chip-containing wafer and a plurality of caps,such as a cap wafer, and the joined structures then severed to formindividual capped chips. This process permits the cap wafer and thechip-containing wafer to be joined at room temperature or at most, aminimally elevated temperature, i.e., without requiring heating to atemperature sufficient to cause the flowing of a fusible material suchas solder. Such process is advantageous, in order to avoid problems ofdifferential expansion between the chip-containing wafer and the capwafer, e.g., when the two wafers are not CTE matched.

The masses of fusible material are provided, for example, by screenprinting a controlled amount of solder into each through hole of the capwafer. Alternatively, the masses of fusible material can be provided bycontacting a cap wafer having tapered through holes wettable by solderwith a bath of solder, such that the solder is drawn onto the wettablesurfaces of the through holes, to fill the through holes with thesolder. The through holes are preferably tapered, either in the mannershown, i.e., growing smaller from the top surface 105 towards the bottomsurface 103, or alternatively, growing smaller from the bottom surfacetowards the, top surface. In another alternative, the through-holes aretapered from both the top and bottom sides, growing smaller towards amiddle of the thickness of the through holes 104. The application of thesolder results in the mass 314 of solder having a protrusion 315extending beyond the bottom surface 103 of the cap. The protrusion 315can be a natural consequence of applying the solder in liquid, e.g., asa solder paste, or in a molten state. In either case, due to surfacetension, a sessile drop forms which causes the protrusion 315 to appear.The protrusion 315 provides a surface which displaces some amount of theconductive adhesive upon bringing the cap together with the chip, suchthat the solder mass 314 fully contacts the conductive adhesive 316. Theconductive adhesive is preferably an anisotropically conductiveadhesive, which conducts in a vertical direction by way of conductiveelements in the adhesive that are pressed into contact with the soldermass 314 and the bond pad 208. As also described and shown below withreference to FIG. 10B, an anisotropically conductive adhesive does notconduct in a lateral direction 317 due to lateral spacing between theconductive elements of the adhesive.

In a variation of this embodiment, as shown in FIG. 3P, a viscous,nonconductive adhesive 318 is applied to the vicinity of the bond padused. In this case, the protrusion 315 of the pre-formed solder mass 314displaces the nonconductive adhesive so as to contact the upper surfaceof the bond pad. The nonconductive adhesive functions to maintain thesolder mass 314 in contact with the bond pad 208. Application of aslightly elevated temperature may be performed to cure and/or shrink thenonconductive adhesive 318, so as to better maintain the contact betweenthe protrusion 315 and the bond pad 208.

FIGS. 3Q an 3R illustrate further variations of this embodiment, inwhich additional protruding features are added to the cap wafer in eachcase, in registration with the through holes 104, such protrudingfeatures provided to assure the quality of contact between the preformedconductive interconnect structures provided in the cap wafer 102 and thebond pads of the chips 102. Specifically, in FIG. 3Q, the protrudingfeature includes a stud bump 324 which is applied to the cap wafer 102at the location of the through hole 104. In a particular embodiment, thesolder mass 314 is planarized, e.g., by polishing, after which the studbump 324 is applied to make the structure shown. Embodiments includingstud bumps are described in greater detail below throughout the presentapplication. In FIG. 3R, the solder mass 314 does not completely fillthe through hole. In such case, the protruding feature 326, e.g., a studbump fills the remaining space within the through hole to project beyondthe bottom surface 103 of the cap 102. Although. FIGS. 3Q and 3Rillustrate structures in which a conductive adhesive is used, i.e., apreferably anisotropic conductive adhesive, a nonconductive adhesive canbe used instead, in the manner as described with reference to FIG. 3P.

FIGS. 3S through 3V illustrate a particular embodiment of a method bywhich a structure 360 including capped chips, in wafer form, are severedinto individual capped chips.

As noted above, a cap wafer and a chip-containing wafer need not consistof the same or similar materials. For example, a chip-containing waferconsisting essentially of silicon may be joined to a cap wafer whichconsists essentially of glass. In such case, a difficulty arises in themanner in which the structure including the cap wafer, as joined to thechip-containing wafer, can be severed into individual capped chips.Conventionally, a silicon wafer can be cut by sawing using a 25 μm wideblade, which saws through the thickness of the wafer at a rate of 70 mmper minute. On the other hand, a glass wafer, having an exemplarythickness of 325 μm, must be cut using a blade having a thickness of 75μm, which also cuts at a comparable rate. The blade optimized forcutting a silicon wafer will cause chipping if used on the glass wafer.Conversely, a blade optimized for cutting a glass wafer producesunsatisfactory results when used to cut a silicon wafer.

In order to cut through a structure including both the silicon wafer andthe glass wafer, a poor compromise is presented. A sawing processcapable of cutting both silicon wafer and glass wafer together operatesat a rate of only 5 mm per minute, which is unacceptable, given thethickness of the combined structure, which is in the hundreds ofmicrons. In addition, typically, dozens of cuts are required to severall chips of such wafers into individual units.

FIG. 3S illustrates an improved method of severing the structure 360into individual units according to an embodiment of the invention. Inthis embodiment, a sealing material 206 is disposed between thechip-containing wafer and the cap wafer, the sealing material 206 beingsuch as that described above with reference to FIG. 2A or in otherabove-described embodiments. The cap wafer 100 and the chip-containingwafer 200 are spaced from each other by a distance. In one embodiment,the distance is controlled, for example, by features of the cap wafer orthe chip wafer which protrude beyond the opposing surfaces 216, 103 ofthe cap wafer or the chip wafer, respectively, as described in greaterdetail below with reference to FIG. 23. Alternatively, the sealingmaterial can include spacing elements, e.g., spheres, for maintaining aminimum distance between the chip and the cap wafer.

The structure 360 is sawed, first by a saw optimized for cutting one ofthe wafers, and thereafter by a saw which is optimized for cutting theother one of the wafers. For example, a saw having a thick blade is usedto produce the wide cut 362 first, cutting through the glass cap wafer100, as shown in FIG. 3S. Such cut 362 may touch the sealing material206, but does not cut through the sealing material. This sawingoperation is preferably then repeated to make all of the cuts throughthe glass across throughout the cap wafer. As stated above, this sawingoperation, being optimized to the glass, proceeds quickly for thatreason. Thereafter, a saw having a relatively narrow blade is applied tomake the narrower but 364, as shown in FIG. 3S. In this case, the bladeand the sawing operation are optimized to cutting the silicon wafer,Preferably, this cut is performed to cut all of the way through thesilicon wafer and through the remaining sealing material. In such case,given the greater width of the cut 362 in the glass wafer 100, thenarrower cut 364 meets the wide cut 362 to complete the severing of thechip. Beneficial results are provided, in that the rate of sawingthrough each wafer separately is at about one order of magnitude or moregreater than the rate of sawing through a combined structure 360 using asingle saw. Thus, the rate of severing the chips is at least severaltimes faster, for example, about 5 to 10 times faster, when the methodaccording to this embodiment is utilized, as compared to using one bladecapable of cutting through both wafers.

FIG. 3T illustrates an individual capped chip 300, diced using thisembodiment of the invention. As shown therein, the edges of the chip 366and the cap 368 of the capped chip unit 300, are not perfectly aligned.This is a consequence of the two separate sawing operations that areperformed. Perfect alignment and orientation of the separately performedsawing operations is difficult, if not impossible, to achieve. FIGS. 3Uand 3V are plan views illustrating the capped chips, after sawing theminto individual units. Some displacement in one or more axes of thedicing lines 370, 372 produced by the two sawing operations is likely tooccur, as shown in FIG. 3U. Angular displacement of one sawing operationrelative to another sawing operation, may also cause angulardisplacement of the dicing lines 370, 372, as shown in FIG. 3V.

FIGS. 4A and 4B are a sectional view and a top-down view, respectively,illustrating a particular embodiment of a capped chip 430 in which theelectrical interconnects 303 are conductively connected by a trace 434formed on the top surface of the cap 102, such as for the purpose ofredistributing an electrical connection. In such embodiment, the trace434 extends from a bonding layer 106 provided on the sidewall through athrough hole at one electrical interconnect 303 a to a bonding layer 106provided at another electrical interconnect 303 a. The trace 434 can beformed at a separate time as the bonding layer 106 or simultaneouslywith the bonding layer 106. As shown in FIG. 4A, a sealing medium 432 isprovided between the cap and the chip 202 in an area underlying thethrough hole 436. When a fusible conductive material is placed inthrough hole 436, as well as through hole 438 and heated, the materialforms a solid bonded connection to the bonding layer 107 and forms anelectrically conductive connection between the bond pad 208 and theelectrical interconnect 303 b. Note that during such process, thefusible material does not flow from the through hole 436 onto the chipbecause of the seal medium 432 which blocks the material from flowinglower than the bottom surface of the cap 102. Alternatively, if thearrangement permits two bond pads of the chip to be at the samepotential, e.g., such as for the distribution of power or groundconnections, the chip may include a bond pad underlying the through hole436, and the sealing, medium 432 not be disposed under through hole 436,such that the electrical interconnect 303 b is also bonded to that bondpad.

FIGS. 4C-4D are a sectional view, and a plan view, respectively,illustrating a variation of the capped chip structure 100 discussedabove with reference to FIGS. 4A-4B. With reference to both figures, inthis structure, a redistribution trace 440, which may function as a“fan-out” trace, is provided on the side 103 of the cap 102 which facesthe chip 202, that is, the underside of the cap, also referred to hereinas the “bottom side” of the cap. The redistribution traces can functionas a “fan-out” trace for the purpose of providing contacts on the capwhich are disposed farther apart and at more convenient locations forhigher level packaging than the locations of the bond pads of the chip.Such arrangement permits the size of the chip to be made smaller, whichallows more cost-effective chip processing, because more chips arefabricated at a time on a single wafer. The cap 102 is provided of amaterial such as that described above, and is preferably mounted to thechip as a plurality of attached caps in wafer form to a plurality ofattached chips of a chip-containing wafer, after which the joinedstructure is severed into individual units.

With specific reference to FIG. 4C, the redistribution traces 440 extendalong the underside 103 of the cap from the locations of interconnectingmasses 442 of conductive material which extends from the bottom side 103to the top side 105 of the cap 102 by way of through holes 104. Theconductive material forming the masses 442 is a flowable conductivematerial such as a conductively loaded polymer, one or more metals or afusible conductive medium. Most preferably, the masses 442 are formed ofa fusible conductive medium such as solder, tin or eutectic composition,and are formed in contact with a bonding layer 107 disposed on walls ofthe through holes. At the other end of the conductive traces,protrusions 444, such as stud bumps, are preferably provided. Theprotrusions 44 provide surfaces to which a bonding medium such as aconductive adhesive 446 adheres to form an electrically conductive pathfrom the bond pads 208 of the chip 202 to the traces 440. Preferably,the adhesive is an anisotropic conductive adhesive, such as thatdescribed above with reference to FIGS. 3O-3R. Alternatively, anonconductive adhesive can be used in place of the conductive adhesive446, in a manner such as that described above with reference to FIG. 3P.Alternatively, a fusible conductive medium such as solder is used inplace, of the conductive adhesive. In such case, a mass of fusiblematerial such as solder is preferably applied as a bump to theprotrusion 444 or the corresponding location of the trace 440, if theprotrusion is not present, before the cap wafer is bonded to the chipwafer. The cap wafer and the chip wafer are then heated to cause thesolder to reflow, thus forming a solder mass bonding the two wafers inthe place where the conductive adhesive 446 is shown.

In one embodiment, the cap wafer is formed by patterning a layer ofmetal on the cap wafer to form the redistribution traces 440, afterwhich the through holes are formed by an etching process or otherremoval process which is endpointed upon reaching the redistributiontraces 440. Bonding layers 107 are then formed on walls of the throughholes, as needed, and the through holes are then are then filled withthe conductive material, that material preferably being a fusibleconductive material such as solder.

FIGS. 4E is a plan view illustrating an example of a chip 202 whichwould benefit upon redesign, through use of the redistribution schemeillustrated in FIGS. 4C-4D. As shown in FIG. 4E, the chip 202 isrectangular, such that the chip has a long edge 242, and a short edge244. The rectangular shape is used because of the rectangular shape of adevice area 204 of the chip, which may be, or may not be required to berectangular. For example, a charge-coupled device (CCD) array isrequired to be rectangular for capturing images. In such chip 202,interconnection wiring 246 carries signals from points 248 connected tothe device area 204 to bond pads 208 of the chip 202. However, therectangular shape of the chip is not optimum, because a greater numberof chips having the same amount of area could be fabricated on a singlewafer, and thus, be fabricated more cost-effectively, if the chips hadsquare shape. Moreover, it is more difficult to form interconnections toa package including the chip by way of wire-bonding when the contacts ofthe package are provided at positions which may vary in two degrees offreedom. For example, as shown in FIG. 4E, the positions of the bondpads 208 of the chip vary vertically along the short edge 244 of thechip 202. Other positions of the bond pads vary horizontally along thelong edge 242. These positions of the bond pads 208 of the chip arereflected in corresponding positions of the contacts of a package (notshown), e.g., a capped chip which includes the chip, which are alsodisposed at different vertical positions along a short edge of thepackage, and at different horizontal positions along a long edge of thepackage.

Faster, more effective, and/or higher quality wire bonding can beachieved if the contacts of the package, and thus, the bond pads 208 ofthe chip are disposed in lines which extend in either horizontal orvertical directions, but not both. In such way, when the wire-bonderforms a bond wire to each location, it is only required to move betweenrespective horizontal locations along each line.

Accordingly, as illustrated in FIG. 4F, in an embodiment of theinvention, wiring 252 extends from the connection points 248 to bondpads 254 which are disposed at different horizontal locations along oneof the horizontal (long) edges 242 of the chip 256.

The above-described embodiment, showing caps having redistributiontraces disposed on the underside of the caps, is desirably employed withchips having a design such as that shown in FIG. 4F, the caps providingany redistribution of signal way that is made necessary by the differentlayout of the bond pads on the chip.

The flowing on and bonding of a fusible conductive material such assolder in the manner discussed in the foregoing with reference to FIGS.1-3N and 4A-4B applies to chips which have bond pads that includeexposed regions which are wettable by solder or other fusible material.In some types of chips, particularly those having aluminum bond pads,and some types of SAW device chips, the bond pads are not wettable bysolder or other such fusible material, in the form that the chips areavailable when packaged. Aluminum bond pads oxidize under ordinaryatmospheric conditions to form a surface layer of alumina which isgenerally not wettable by a molten mass of solder. On the other hand,some types of wafers, especially III-V compound semiconductor wafers,include bond pads which are formed of or include an outer layer of gold.Here, a different problem exists in that the gold of the bond pad issubject to being dissolved by solder and other fusible materials, whichpotentially destroys the bond pad to cause an open circuit between thebond pad and the connecting trace.

One way that these concerns is addressed is to specifically form abonding layer on the bond pads 208 of the wafer prior to joining the capelement to the wafer, the bonding layer being wettable by solder (orother fusible material to be used). Such bonding layer can be formed bya process such as that used for forming an “under bump metallization”(“UBM”) on a chip. However, some types of chips, particularly SAWdevices, are very sensitive to contamination and can be degraded byprocessing used to form bonding layers.

Accordingly, in an embodiment of the invention illustrated in FIG. 5A,such concern is addressed by forming bonding layers on bond pads of achip or wafer after the cap element has been joined to the wafer. Asshown in FIG. 5A, in such embodiment, the joined assembly of the wafercontaining the chip 202 and the cap 102 is placed in a chamber in whichit is subjected to deposition of one or more materials to form a bondinglayer 540, e.g., a UBM on the surface of the bond pad 208. A mask, e.g.,a contact mask, may also be positioned over the cap 202 such that onlythe through holes 104 are exposed during the deposition. Otherwise, thedeposited material can be removed from the top surface of the cap 202after the chip has been joined to the cap and the electricalinterconnects 303 have been formed. During such deposition, the cap 202also functions as a shadow mask to prevent the deposition of the UBM onthe device region 204 of the chip 202.

As a result of the deposition, a bonding layer 106 may also besimultaneously formed on the sidewalls 107 of the through holes 104.During such process, dielectric oxide present on the surface of the bondpad 208 is removed.

A limiting factor of the embodiments described above with respect toFIGS. 1-3D is that it requires the solder ball 302 (FIG. 3A) to meltduring the reflow process in such way that the meniscus (not shown) ofthe molten solder ball hangs low enough to touch the UBM coated bond pad208, and thereby establish a solder bond with the bond pad 208. Whetheror not the solder bond is established depends on several factors,including the volume of the molten solder ball, the size of the openingof the through hole 104 which faces the chip, and the height 125 of thespacing between the chip 102 and the cap 101, requiring tolerances onthe process to be relatively tight. In addition, such, process allowslittle freedom to choose the height 125 of the spacing between the cap102 and the chip 202. Desirably, such height is determined by thefunctionality sought to be obtained by placing the cap over the devicearea of the chip, such as when the device area includes a SAW device orMEMS device which requires a cavity.

The embodiment, shown in FIGS. 6A-6B addresses this concern. In thisembodiment, conductive stud bumps 662 are applied to the bond pads 208of the chip, which is best performed while the chip is in wafer form.Thereafter, the cap element is aligned to the wafer and sealed thereto.During the alignment step, the stud bumps, particularly if they containrelatively thick shafts, can assist in the process of properly aligningthe cap element to the wafer, as the stud bumps 662, when aligned, stickup at least partially through the through holes 106. Stud bumpscontaining certain metals may be applied directly to bond pads withoutfirst applying a bonding layer such as a UBM, thus providing a furtheralternative way of forming conductive interconnects to bond pads whichare not directly wettable by solder. For example stud bumps consistingessentially of one or more of copper, nickel, silver, platinum and goldcan be applied this way. When wettable bonding layers are provided onbond pads, stud bumps of solder or other fusible conductive materialscan be used.

A process such as that described above relative to FIGS. 3A-3B is thenused to form electrical interconnects 663 which include stud bumps andthe fusible material so as to extend from the bond pads 208 through thethrough holes 665. As in the embodiments described above, a sealingmedium 664 is provided between the chip 202 and the cap 102. One problemwith some sealing media is that it is difficult to control the thicknessT of the sealing medium, and thus the thickness of the void 214 betweenthe chip and the cap, simply by controlling the amount of the sealingmedium or the amount of pressure applied to locations of the chip afterthe sealing medium is applied.

This concern is addressed in the embodiment shown in FIG. 6A, in whicheach conductive stud bump 662 has a shoulder 666, on which the bottomsurface 103 of the cap 102 rests, so as to space the bottom surface 103a distance T from the front surface 216 of the chip. As apparent fromFIG. 6A, that distance T includes any thickness T2 of the bond pad 208which extends above the front surface 216 of the chip, as well as thethickness of the lower ‘ball’ portion of the stud bump from the bond pad208 to the shoulder 666.

FIG. 7C illustrates a capped chip 748 according to another embodiment ofthe invention, in which conductive interconnects are provided whichinclude bonding wires 752 which extend from bond pads 208 of the chip202 through openings 754 in the cap 102 to contacts 750 disposed on thetop surface 105 of the cap. The openings 754 can be such as the throughholes 104 described above with respect to FIGS. 1-3D, for example, whichare sized to accommodate one interconnect per through hole, and topermit the bonding of bonding wires 752 to respective bond pads of thechip. Alternatively, the openings 754 can be bonding windows which aresized and shaped, e.g., extending primarily in one linear directionalong the cap, so as to overlie a linearly extending row of bond pads208 of the chip, and permitting the formation of wire-bonds to each ofthe bond pads 208 of that row through the opening. While the peripheraledges of the capped chip 748 are sealed by a sealing material 206, in amanner such as that described above with reference to FIGS. 1-3D, anadditional sealing material 756 is deposited in contact with theopenings 754 of the cap to seal the openings after the bonding wireshave been formed. Such sealing material can include, for example, apolymer which hardens to form a nonconductive region for insulatingrespective bonding wires from each other, while also mechanicallysupporting the bonding wires. In a particular embodiment, the sealingmaterial 756 is an encapsulant which is disposed as an insulating mediumover the top surface 105 of the cap generally, except for the area inwhich the contacts 750 are located. Alternatively, another insulatorsuch as a glass, e.g., preferably a low-melting point glass, is disposedin each through hole to insulate and support the bonding wire. In aparticular embodiment, in which the wire bonds extend through individualthrough holes 104 which are aligned to the bond pads, a mass of aflowable conductive material such as a conductively loaded polymer or afusible conductive material is disposed in each opening 754 to seal theopening in place of a polymer. In such manner, enlarged conductiveinterconnects 758 are formed at the top surface 105 of the cap 102, theinterconnects 758 extending across each opening to seal each openingincluding the area of the contacts 750. In such case, higher levelassemblies can be made by forming appropriate electrically conductivebonds to the thus formed interconnects 758.

FIG. 7D illustrates a variation of the embodiment described in FIG. 7Cin which bonding wires 762 that are joined to the bond pads 208 of thechip are not bonded to contacts on the cap. Instead, the chip is bondedby bonding wires in a face-up orientation to contacts 764 of a packagingelement 760, e.g., any of many types of dielectric elements andsubstrates which have conductive traces thereon. Advances in thecapability of wire bonding machines now permit bonding wires to beformed which have relatively complex profiles, and to be formed reliablyand repetitively. Thus, FIG. 7D illustrates an example in which thebonding wire 762 is formed to extend directly between a bond pad of thechip and a secondary packaging element, e.g., a dielectric panel, orcircuit board, which is farther away from the bond pad 208 than thatshown and described above in FIG. 7C. In this embodiment, the cap 102 ispreferably an at least partially optically transmissive element, thatterm denoting an element which is either somewhat translucent ortransparent to light in a range of wavelengths of interest. Morepreferably, the cap 102 is transparent, consisting essentially of amaterial such as a glass or a polymer, which can be molded. In aparticular embodiment, the cap 102, is molded to contain an opticalelement, e.g., a lens, such as the caps and optical elements describedin commonly assigned, co-pending U.S. patent application Ser. No.10/928,839, filed Aug. 27, 2004, of which this application is acontinuation-in-part.

In this embodiment, the formation of the bonding wires to bond the chipto the packaging element 760 is done after the cap 102 is affixed to thechip 202 by the sealing material 206, and the chip is mounted to thepackaging, element, such as by an adhesive 766, e.g., an adhesivecommonly known as a “die attach” adhesive. Alternatively, a thermalconductor can be mounted between the chip 202 and the cap 102 forconducting heat away from the chip and onto a thermal conductor mountprovided in the packaging element, such as described in commonlyassigned, co-pending U.S. patent application Ser. No. 10/783,314 filedFeb. 20, 2004, the contents of which are hereby incorporated byreference herein. In a particular embodiment, the chip is bonded, in a“chip-on-board” configuration) to a circuit panel, e.g., a printedcircuit board or flexible circuit panel, in place of the packagingelement 760.

The above-described embodiment shown in FIG. 7D can be especiallyadvantageous for the packaging of chips which include optically activeelements, for example, image sensors. Such sensors are especiallyvulnerable to dust or other particle contamination which is most likelyto occur after the chip has been fabricated. Dust or other particleswhich settle directly on the imaging are of the chip can obscure aportion of the pixels of the active imaging area, thus rendering thechip unusable. The method provided in this embodiment reduces the riskof such contamination by providing a protective optically transmissivecover over the chip prior to performing subsequent higher-levelpackaging operations.

In another embodiment, as illustrated in FIG. 7E, bonding wires 774extend from bond pads 208 of the chip to bonding shelves 772 of agull-wing package 770. This packaged chip preferably includes anoptically active chip and an optically transmissive cover 202, such asthat described above with respect to FIG. 7D. An additional package lid776 is mounted to vertical members 778 of the package, the package lid776 desirably also being at least partially optically transmissive, andpreferably being transparent.

In a particular embodiment, as shown in FIG. 7A, a unit 700 includes aconductive interconnect 703 which include a stud bump 662 and aconductive material 704 that seals the stud bump to the cap 102. In thisembodiment, the conductive material 704 is a conductive organic materialsuch as a conductive adhesive or conductive sealant. A conductiveorganic material which is curable at room temperature or a slightlyelevated temperature is advantageously used when the material of whichthe cap is formed is not CTE matched to the chip. In such manner,conductive interconnects 703 can be made to the unit 700 withoutinducing strains in the chip or cap due to CTE mismatch.

As further shown in FIG. 7A, and in the plan view in FIG. 7B, the unit700 may further include a plurality of such conductive interconnects703, which are connected by redistribution or fan-out traces 706, torespective conductive contacts 708. In such manner, signals coming offof the chip 202 are redistributed through the conductive interconnects703 and the traces 706 to the contacts 708 which lie at a fartherdistance away from the device region 710 and closer to the edges 712 ofthe capped chip 700.

As shown in FIGS. 8A and 8B, once a unit 300 including a capped chip hasbeen formed, it may then be aligned to and surface mounted to a printedcircuit, board (PCB) or other type of circuit panel 802 to form anassembly 800. FIG. 8A shows the unit 300 having the fusible material 304of the interconnect aligned to a terminal, e.g., a land 808 of thecircuit panel 802. FIG. 8B illustrates the resulting assembly 800 afterheating to cause the fusible material to be bonded to the terminal 808of the circuit panel 802. While flux is generally utilized for thepurpose of joining materials in an oxygen-containing environment, thejoining process can be performed fluxlessly, under conditions whichinhibit contamination, i.e., by joining the unit 300 to the circuitpanel 802 in the presence of a non-oxygen containing environment such asnitrogen, argon, or a vacuum, for example.

In accordance with some surface mounting practices, extra solder can beapplied to the circuit panel prior to mounting the unit to increase thevolume of solder available to make the connection. Such pre-forms ofsolder can be applied to the terminals of the circuit panel with flux,if needed, prior-to mounting the unit. FIGS. 9A and 9B illustrate suchtechnique. As illustrated in FIG. 9A, due to the process used to makethe capped chip unit 300, the fusible material 916 provided on thebonding layer 917 of the through hole of the unit 300 does notcompletely fill the through hole, but leaves a void 921 in a portion ofthe through hole above the circuit panel 802. By providing a pre-form922 of additional solder or other fusible material on the terminal 920of the circuit panel 802, sufficient solder is provided to provide areliable connection between the unit 300 and the circuit panel. FIG. 9Billustrates the assembly 900 formed by the unit and the circuit afterheating to cause the solder contained in the pre-form and in the throughhole to melt and join, being drawn into the through hole to formconnection 924 to terminal 920. As a result of the added solder from thepre-form, a bulked up solder connection 924 is provided which issufficient to establish a connection to the terminal.

As an alternative to that described above, the solder pre-form can beprovided for use in hierarchically soldering the unit to the circuitpanel. Stated another way, the conductive interconnects of the unit 300can be formed using a solder or other fusible material which melts at ahigher temperature than the solder used to join the unit 300 to thecircuit panel, such that the original higher temperature material doesnot melt and reflow during the subsequent joining operation.

FIGS. 10A and 10B illustrate another method for joining the unit 300 toa circuit panel to form an assembly 1000, in which a conductive adhesive1622 is used to conductively join the unit 300 to a land 1020 of thecircuit panel 1019. FIG. 10A illustrates a stage after which the unit300 has been placed in alignment with the circuit panel 1019, such thatthe solder 1016 in the through hole is positioned over the land 1020.FIG. 10B illustrates a subsequent stage after the unit has been pressedinto contact with the land 1020, causing the conductive adhesive to atleast substantially fill the through hole to form a connection 1018.However, as also shown in FIG. 10B, a certain amount of the conductiveadhesive 1024 flows off the land 1020 onto other areas of the circuitpanel. For this reason, in order to avoid the making of electricalconnections in places where they are not desired, the conductiveadhesive is desirably an anisotropic conductive adhesive 1024, as shownin FIG. 10B. Such anisotropic conductive adhesive contains discreteconductive particles 1026, such as conductive spheres that are normallyspaced from each other by a fluid medium used to carry them. Whenpressed between two objects at a spacing equal to the width of thesphere, the conductive spheres provide an electrical connection betweenthe two objects. However, due to the lateral spacing between theconductive spheres, no substantial electrical connection is provided ina lateral direction which runs between the surfaces of the two objects.

FIG. 11A illustrates a variation of the embodiment shown above in whichthe unit 300 includes a bonding layer 1124 which extends from inside thethrough hole 1104 to have an extension 1126 extending on the mountingface 1107 of the unit 300. The extension 1126 is preferably provided asan annular ring surrounding the through hole 1104. The extension 1126provides additional surface area for retaining solder 1116, prior to andafter the unit 300 is bonded to the circuit panel 1119. The extension1126 and a larger amount of solder adhering thereto on the unit 300, canmitigate against having to provide additional solder on the terminal1120 of the circuit panel, as discussed above with respect to FIG. 10A.

FIG. 11B illustrates yet another variation in which unit 300 includes anextension 1128 of the bonding layer 1126 on the surface 1105 of the cap1106 which faces the chip 1102. During the joining process of the cap tothe chip, the extension 1128 draws solder from inside the through hole1104 onto itself to bring it closer to the bond pad 1114 of the chip1102. This, in turn, assists in forming the bond between the cap 1106and the chip 1102.

FIGS. 12-17 illustrate a particular variation of the process describedabove with respect to FIGS. 1-3D and 8A-8B, or one of the alternativesshown in FIGS. 9A-11B for making a unit and joining it to a circuitpanel. A “lid”, like the “cap” described in the foregoing, refers to anarticle that is mounted as a cover over the front surface of a chip.

Some types of chips, particularly chips which include an electro-opticdevice, need to be packaged with a cap which is at least partiallyoptically transmissive. The term “optically transmissive” is used torefer to a material that is either optically transparent or opticallytranslucent in a range of wavelengths of interest, whether suchwavelengths of interest are in a visible, infrared or ultraviolet rangeof the spectrum. For example, electro-optic imaging chips includingcharge-coupled device (“CCD”) arrays require a lid which includes anoptically transmissive package window, in order to prevent dust or otherparticles from landing on the CCD array, which would optically impairand obscure pixels of the CCD array. Such lid can also be used toprotect against damage due to corrosion by atmospheric contaminants,particularly water vapor. The lid can be of any suitable opticallytransmissive material, including but not limited to glass, polymer andsemiconductors. After the chip is joined to the lid, a turret or trainassembly containing a lens, and optionally infrared (IR) and/orultraviolet (UV) filters is joined to the lid, e.g., as by welding,adhesive bonding or use of a fusible material such as solder.

In this variation, a sacrificial coating is applied to a surface of alid prior to joining the lid to a chip, in order to protect the lidagainst contamination. The sacrificial coating is then removed later,after steps are performed to join the lid to the chip to form a unit tojoin that unit to a circuit panel. As above, while the process isdescribed here in terms of joining a lid to a chip, it should also beunderstood, with appropriate modifications, to apply to the joining of alid element containing multiple attached lids to a wafer or othersubstrate which includes multiple attached chips, after which the joinedlid element and wafer are severed along dicing lanes to formindividually lidded chips.

When a lid is joined to a chip by one of the above-described processes,steps to bond the lid to the chip can introduce contaminating material.Thereafter, steps to join the lidded chip to a circuit panel canintroduce further contaminating material. Contamination can result fromthe environment in which the chip is packaged or, from the nature of theprocess itself that is used to perform the joining processes. Forexample, a joining process that involves solder with flux can produceresidual material that is undesirable to leave on the surface of thecap. Other methods of bonding a lidded chips

Accordingly, as shown in FIG. 12, a sacrificial coating 1252 is appliedto the surface of an optically transmissive lid 1250. The sacrificialcoating 1252 is a material which can be applied and remain through thesteps of bonding the lid to the chip, but then be removed to leave thesurface of the lid in a clean condition without degrading the conditionof the joints of the assembly. In the embodiment shown in FIG. 12, thesacrificial coating includes a photosensitive resist film, suitable foruse in subsequent photolithographic patterning of the lid. Such resistfilm is best chosen with regard to the etchant which will be used topattern the material of the lid, which can vary between inorganicmaterials such as glasses and organic materials such as polymers. Forexample, an etchant such as fluorosilicic acid is suitable forpatterning a lid which is formed of glass, especially lids which areformed of a glass which has been doped to facilitate chemical etchingsuch as borosilicate glass. In such case, a spin-on photoresist or hotroll laminate photoresist is suitable for use in etching of glass. Suchphotoresists are also not degraded by temperatures at which soldersmelt, nor by fluxes used in soldering processes. However, suchphotoresists are also readily dissolved and cleared from a surfacethrough organic solvents.

FIG. 13 illustrates the patterned photoresist film 1252, after it hasbeen exposed and developed to produce openings 1254 in the photoresistlayer 1254. Thereafter, as shown in FIG. 14, the lid is etched, usingthe patterned photoresist film as a mask to produce through holes 1256.

Thereafter, as shown in FIG. 15, further steps are performed to depositbonding layers 1258 on the sidewalls 1260 of the through holes. Thebonding layers 1258 are provided for the purpose of permitting a fusiblematerial such as solder, tin, etc. to be bonded to the through holes ofthe lid 1256, in a manner as described above with respect to FIGS. 1-3D.During the deposition, a contact mask may be placed over the photoresistfilm 1252 as needed, to prevent the photoresist film from being sealedwithin the bonding material, which might interfere with its laterremoval depending on the type of resist. Such bonding layer is provided,for example, by deposition including electroless plating or electrolessplating followed by electroplating. Alternatively, the bonding layer isprovided through vapor phase deposition, i.e., any one of manydeposition processes such as physical vapor deposition (PVD), chemicalvapor deposition and the like.

A subsequent stage of fabrication is shown in FIG. 16, after the lid1250 has been joined to a chip 1264 by a set of electrically conductiveinterconnects 1262, and after the interconnects of the lidded chip havebeen joined to a circuit panel 1264. The circuit panel 1264 includes anopening 1266 or, alternatively, a window consisting of an opticallytransmissive material, disposed in alignment with the electro-opticdevice 1268 of the chip 1264 to provide an optically transmissive pathto and from the electro-optic device 1268. The circuit panel 1264 can beof any type, being either rigid, semi-rigid, or-flexible. In oneembodiment, the circuit panel 1264 is flexible and has a flexibledielectric element on which conductive traces are disposed.

As also shown in FIG. 16, one result of the prior joining processes isunwanted residual matter 1270, e.g., particles, flux or adhesiveresidue, etc., that remains on the surface of the photoresist film 1252.As illustrated in FIG. 17, the residual matter is then removed in stepsused to remove the photoresist film, such as through washing of theassembled circuit panel and the lidded chip in an organic solvent inwhich the film is soluble. This results in an assembly 1272 in which thecontaminating material has been removed, and which is now ready forsteps to provide a higher order assembly. Thereafter, a turret, train orother optical element, may be mounted above the opening 1266 in thecircuit panel 1264.

The process shown and described above can be modified in severalalternative ways. In one alternative process, the lid is patterned bylaser drilling rather than chemical etching. The laser drilling isperformed after the sacrificial coating is applied, at which timematerial ejected from the drilled openings collects on the sacrificialcoating. Thereafter, the ejected material is prevented fromcontaminating the lid when the sacrificial coating is removed from thesurface of the lid.

In another embodiment, the sacrificial coating need not be a photoresistfilm and the coating need not patterned to provide a mask for etchingthrough holes in the lid. Rather, in such embodiment, the sacrificialcoating is provided on a face of the lid, and thereafter, the lid ismounted to the chip, such as through a sealing medium or fusibleconductive medium as described above. The lidded chip is then mounted toan additional element such as a circuit panel, or alternatively, aturret, or ‘train’, as described above. Thereafter, the sacrificialcoating is removed, removing with it residual matter remaining from theprior steps used to mount the lid to the chip and the lidded chip to theadditional element.

In a particular form of such embodiment, the sacrificial coating is onethat is mechanically releasable from the surface of the lid, such as bypeeling. For example, such film can be provided of an adhesively backedplastic, polymeric film capable of withstanding the processes used tojoin the lid to the chip and that which joins the combined unit toanother element. For example, materials such as those used in theadhesive of removable self-stick notepaper and in food-wrap film appearsuited for this purpose. Alternatively, the peelable film can be a metalsuch as molybdenum or other metal or other rigid or semi-rigid polymer.

A limiting factor of the embodiments described above with respect toFIGS. 1-3D, for example, is that the lateral spacing between adjacentthrough holes might not be optimal. Increasing integration density ofchips and corresponding decreases in the spacing between adjacent bondpads of a chip demand that a cap to be mounted to the chip havecorrespondingly decreased spacing between interconnects. Referring toFIG. 3C, the through holes 104, of the cap 102 are shown tapered onlyfrom the top surface 105 of the cap, such that a sidewall 107 (FIG. 1)is oriented at an angle typically ranging from about 5 degrees to 70degrees from the vertical (the vertical being the direction which isnormal to the top surface 105). More preferably, the angle of thesidewall (FIG. 1) to the vertical is between 20 degrees to 60 degreesand, most preferably at an angle between 30 degrees and 60 degrees, suchthat the diameter of the through holes 104 varies between a smallerdiameter 330 at the bottom surface 103 and a larger diameter 335 at thetop surface 105. Typically, a wet chemical etching process applied tothe cap wafer 100 which consists essentially of silicon results in thesidewall 107 making an angle to the vertical of between 20 and 60degrees. However, laser drilling is another process used to form throughholes in a cap wafer which is provided, for example, of silicon, glass,ceramic or other similar material, typically results in an angle of 7degrees relative to the normal. The angle that the sidewall makes withthe top surface 105 is desirably made small, in order to reduce theamount of area occupied by each interconnect, due to the increased pitchof through holes that have a larger angle, as is described in moredetail below with reference to FIG. 18. The variation in diametersbetween the through hole at the top surface 105 with respect to thebottom surface 103 assists the fabrication method as a way of initiallyholding the solder ball 302 (FIG. 3A) (which is larger than the smallerdiameter 330) in place inside the through hole 104. Depending upon thethickness of the cap 102, which, illustratively, ranges between 100 and300 μm, and the smaller diameter 330 of the through holes, which istypically on the order of 70 to 100 μm, the larger diameter 335 of thethrough holes may range from twice as large to many times larger thanthe smaller diameter 330.

When considered in terms of forming interconnects to closely spaced bondpads 208 of a chip 202, it is seen that the larger diameters 335 of thethrough holes at the top surface 305 of the cap may well limit thespacing at which such interconnects 303 can be made. This concept isbest illustrated with respect to FIG. 18. FIG. 18 illustrates threeindividual caps 400, 402 and 404, respectively, in which through holes410, 412, and 414, respectively, have been patterned differently, and inwhich the pitch between adjacent through holes varies significantlyaccording to the method used to pattern the caps. Thus, cap 400, havingthrough holes 410 which are tapered from only one surface, i.e., the topsurface 405, has the largest pitch 407, because of the large diameter403 of the through holes 410 that exist at the top surface 405. Throughholes are ordinarily tapered from one surface of the cap by isotropicetching from that one surface. On the other hand, cap 402 has smallerpitch 409 because its through holes are tapered from both the topsurface 415 and the bottom surface 417 of the cap 402, such that theprofile of the through holes includes an internal edge 413. Such taperis typically achieved by etching the through holes 412 simultaneouslyand isotropically from both the top and bottom surfaces of the cap 402.In some cases, depending upon the degree to which the through hole isetched in a lateral direction (being the direction parallel to thediameter 409) the internal edge 413 can acquire the appearance of a“knife edge”. Cap 404 illustrates a case in which through holes 414 arepatterned without tapering, having straight, vertical sidewalls. Thepitch 419 of through holes 414 of the cap 404 is the smallest of thepitches 407, 409, 419, because of the straight, vertical profile of thethrough holes 414.

However, the profiles of the through holes of cap 402 and cap 404 aresuch that they do not permit the same techniques to be used as describedabove relative to FIGS. 1 through 3D when joining the cap 402 or 404 toa chip. Solderable metallizations cannot be easily provided on sidewallsof the through holes 412 of cap 404 by the patterning processesdescribed above, which are conventionally used in conjunction with vaporphase deposition and wet electrochemical processes to make the taperedthrough holes as described above relative to FIGS. 1 through 3D. Thesepatterning processes cannot be performed from just the top surface 415or the bottom surface 417 of the cap, because patterning will beachieved only on surfaces that face up, i.e. only the surface of thethrough hole above the internal edge 413 and upward, including the topsurface 415 of the cap 402. This precludes the portion of the throughhole below the internal edge 413, i.e., facing towards the bottomsurface 417 from being properly metallized. In the case of cap 404, thevertical, straight profile of the sidewall 418 of the through hole 414makes it difficult to achieve a suitable metallization. However, in thecase of cap 402, the knife-edge through hole profile can still be usedto form a capped chip having electrical interconnects which include studbumps extending from the bond pads, similar to that described above inrelation to FIG. 6A. In such case, only the portion of the through hole412 that is tapered towards the top surface 415 need be metallized. Thisrequires the stud bump (662 in FIG. 6A) to protrude upwardly through thethrough hole 412 past the knife-edge 413 in the cap 402. On the otherhand, the necessity for the through hole 412 to have a bonding layer 106(FIG. 6A) on the sidewall thereof is diminished if another flowableconductive medium such as an organic medium is used in place of thesolder.

FIGS. 19 through 22 illustrate stages in a method of joining a cap to achip according to one embodiment of the invention. FIG. 19 shows a cap500 in an inverted position during fabrication, the cap 500 having abottom or inner surface 502, a top or outer surface 504, and throughholes 510. These designations of the bottom (inner) and top (outer)surfaces refer to the orientation in which the cap will be mounted tothe chip, when steps to complete the bonding of the cap to the chip areperformed, as shown in FIGS. 21-22. In this embodiment, the throughholes are preferably tapered so as to become progressively smaller fromthe bottom surface toward the top surface. As such, the tapered throughholes are substantially frusto-conical in shape. The tapering of thethrough holes 510 is not absolutely necessary. Tapered through holesassist in achieving some of the potential benefits available by thejoining process, as will be apparent from the description below.

In this inverted position, solderable metallizations 515 are formed onthe sidewalls 520 of the through holes 510, as by conventionalvapor-phase or wet electrochemical processing directed towards thebottom surface of the cap 500, as described above. In one embodiment,the solderable metallizations optionally extend onto a portion 525 ofthe bottom surface of the cap 500 surrounding each through hole.

FIG. 20 illustrates processing performed to a chip 600 to which cap 500is to be mounted, the chip having solder-wettable bond pads 606, adevice region 602 and wiring 604 interconnecting the device region 602to the bond pads. A conductive ball 610 is placed on each metallizedbond pad, preferably by a fluxless process, in order to avoid flux vaporand residue therefrom from potentially contaminating features at thesurface of the chip 600, e.g. the device area 602. A process is thenconducted to bond the conductive ball 610 to the chip 600. In apreferred embodiment, the conductive ball is a solder ball, consistingessentially of a solder or other fusible conductive material, e.g., oneor more of tin, lead, or eutectic composition or layered arrangement ofsuch metals or other metals, which is adapted to generally soften orliquefy upon being heated to a reflowing temperature, which isrelatively low. FIG. 20 illustrates the chip after a solder ball 610 hasbeen placed on each bond pad 606 and bonded thereto by a process whichis characterizable as “reflowing”. After reflowing, the solder ballstypically retain a shape that is essentially spherical. The temperatureof the solder balls is then lowered again for the performance of asubsequent step in which the cap 500 is aligned to the chip 600.

FIG. 21 illustrates such further stage in the process. In this stage,the chip 600 is placed such that the front surface 601 faces up. The cap500 is turned over, such that the bottom surface 502 of the cap nowfaces down, toward the front surface 601 of the chip 600. At this stage,the metallized substantially frusto-conical through holes 510 of the cap500 assist in aligning the cap 500 to the chip 600 in a self-locatingmanner. This occurs as follows. Rough alignment is achieved between thecap 500 and the chip 600, such that any misalignment is less than thespacing between the centerlines of the through holes. If the cap 500 isthen allowed to rest on, the chip 600, the through holes 510 will alignthemselves to the solder balls 610, causing the through holes of the cap500 to drop down onto the solder balls 610, thus self-locating thethrough holes 510 to the solder balls 610. Misalignment between the cap500 and the chip 600 is subject to variation in two horizontal degreesof freedom (X) and (Y), in three rotational degrees of freedom: turningin the horizontal plane (yaw), forward or backward tilt (pitch) andside-to-side tilt (roll), and in a vertical degree of freedom, i.e.vertical displacement (Z). The self-locating mechanism described hereinaligns the cap to the chip with respect to all of these degrees offreedom at the time that the cap 500 is placed on the chip 600.

In the stage shown in FIG. 22, a process is conducted to bond theconductive balls 610 to the metallizations provided in the cap 500. Whenthe conductive balls are solder balls 610, this is preferably conductedas a reflowing process, which causes the material of the solder balls610 to be drawn further into the through holes 510. As a result of thisreflowing process, the solder balls 610 preferably extend somewhat abovethe top surface 504 of the cap 500. As also shown in FIG. 22, the cap500 is desirably sealed to the chip 600 by a sealing material 810 whichsurrounds the device region and the region which includes the bond padsof the chip 600. The sealing material preferably includes a materialsuch as that described above with reference to FIG. 2A.

During such reflowing process, due to the fluid nature of the solderballs 610, means preferably are provided for maintaining a desirablevertical spacing between the opposed surfaces 502, 601 of the cap andthe chip. In one embodiment, one or more spacer elements areincorporated into the sealing material. For example, an adhesive sealingmaterial can include spherical or fibrous elements which deform little,thus maintaining a predetermined spacing between the opposed surfaces.In a particular embodiment, a spacer structure is incorporated into oneor the other of the cap and the chip. For example, as shown in FIG. 23,a spacer may take the form of a ridge 900 formed as part of the cap 500,the ridge 900 having a knife-edge 902, which is allowed to rest on thefront surface 601 of the chip 600. A sealing material 910, such as anadhesive, can be disposed in contact with the ridge 900, as shown inFIG. 23. Otherwise, the sealing material can be displaced from thelocation of the ridge 900. The ridge 900 allows the cap 500 to bepressed to the chip, e.g., pressure clamped, during the joining processfor any of the above-listed sealing materials, while the ridge maintainsa desired spacing between the cap 500 and the chip 600. When the aboveprocessing is performed simultaneously on an array of attached chips andattached caps, the packaged chips are thereafter diced, i.e., severedinto individual packaged chips.

FIG. 24 illustrates a variation of the embodiment described above, inwhich the metallization of the cap to provide a bonding layer extends asan annular structure 1004 disposed on the bottom surface 1002 of a cap1000. In one embodiment, an annular structure 1004 is formed bydeposition through widened openings of a masking layer (not shown) onthe cap through which material is deposited in an additive process toform the metallization, in comparison to those used to form themetallizations shown in FIG. 1. Alternatively, the annular structure1004 can be formed by decreasing the size of mask patterns disposedbetween the annular structures, when metallization patterns are formedby a subtractive process following the formation of a metallizationlayer over the cap. FIG. 25 illustrates a packaged chip 1150 showing afurther variation in which the conductive balls 1144 are of a type whichremain substantially rigid upon heating to a bonding temperature, orhave a core which remains substantially rigid. In such embodiment, theconductive balls 1144 are used to maintain a desirable vertical spacingbetween the cap 1000 and the chip 1142. A solder bond or diffusion bondcan be provided between a metal disposed at an exterior of theconductive ball and the metallization layer 1001 of the cap 1000 andalso between such metal and the metallization 1141 of the chip, forexample. Joining at this location may also be accomplished using anelectrically conductive organic material.

As further shown in FIG. 25, solder or other conductive material 1145 isprovided to fill the space between the conductive ball and the topsurface 1006 of the cap 1000. In a particular embodiment, an additionalseal 1130 can be provided over the peripheral edges 1042, 1140 of thecap and the chip, respectively, by depositing an additional sealingmaterial. The additional seal 1130, which desirably also covers thealready provided sealing material 910, may be provided for the purposeof achieving hermeticity, electrical isolation, or other such purpose.The additional seal also preferably extends onto the top surface 1006 ofthe cap and the rear surface 1146 of the chip.

FIG. 26 illustrates a further embodiment in which the packaged chip 1150shown in FIG. 25 is mounted to a circuit panel 1202 having one or moreterminals 1204 and traces 1206 disposed thereon. The mounting shown inFIG. 26 is through a solder bond between the solder or other conductivematerial 1145 present at the top surface 1006 of the cap 1000 and masses1205 of solder disposed on the terminals 1204 of the circuit panel 1202.

With reference to FIG. 27, another embodiment of a method of making acapped chip having vertical interconnects is shown in which the throughholes 1310 of a cap 1300 are not required to have solderablemetallizations prior to the cap 1300 being joined to the chip 1302. FIG.27 illustrates a case in which the through holes 1310 of the cap 1300are tapered from both the top surface 1303 and the bottom surface 1305,as described above with respect to FIG. 18. In this embodiment, the chip1302 has stud bumps 1320 disposed on bond pads 1330. The stud bumps 1320provide a surface for bonding of solder or other conductive material toform a vertical interconnect extending upwardly from a chip 1302. Asdescribed in relation to other embodiments above, a “picture frame”ring-seal 1340 seals the gap between the chip and the cap.

The stud bumps 1320 are desirably tapered, as shown in FIG. 27, as canbe provided according to several processes known to those skilled in theart. In this embodiment, the stud bump desirably has a shaft diameter1315 which is close to the mashed ball diameter obtained during theapplication of the stud bump, and a length 1325 that exceeds thethickness of a sealing material 1340 that seals the cap 1300 to the chip1302. For example, the stud bumps can be such as those shown and madeaccording to the process described in U.S. patent Publication No. US2003/0159276 A1, published Aug. 28, 2003, the disclosure of which ishereby incorporated herein by reference. Tapered stud bumps are morecapable of retaining their upwardly extending shape when the cap 1300 isplaced over the chip 1302, such that the stud bumps 1320 are more likelyto maintain registration with the through holes 1310, than if the studbumps had a narrow, much more deformable profile. As such, the studbumps assist the cap 1300 in becoming aligned to the chip 1302 in aself-locating manner, at least on a side-to-side basis, i.e., in atleast the X and Y degrees of freedom. However, as shown in FIG. 27, whena through hole 1310 a is not in perfect alignment with a stud bump 1320a, the taper of the through hole 1310 a allows the stud bump 1320 a todeform somewhat, thus allowing it to at least enter the through hole1310 a. Desirably, stud bumps 1320 protrude through the through hole toextend above the top surface 1303 of the cap.

FIG. 28A illustrates a variation of the embodiment shown in FIG. 27, inwhich the through holes have a straight, vertical profile, rather thanbeing tapered from both sides, as described above with respect to FIG.27. As shown in FIG. 28A, the top surface 1403 of the cap is optionallyprovided with a solderable metallization 1410. The solderablemetallization is preferably provided as an annular structure surroundingeach through hole. FIGS. 28A and 28B illustrate two stages ofprocessing. In an earlier stage of processing, shown in FIG. 28A, asolder ball 1420 is disposed on the metallization 1410, as placedthereon by a prior solder ball stenciling process. A subsequent stage ofprocessing, shown in FIG. 28B, illustrates the reflowed solder ball 1430as joined to the stud bump 1320 by a subsequent reflowing process.During such reflowing process, the solder ball 1430 is drawn onto thesurface of the stud bump 1320 by a solder-wettable metal present at thesurface of the stud bump such as gold, tin or platinum. As a result, thesolder forms a continuous solid electrically conductive mass connectingthe stud bump to the bonding layer 1410 of the cap and sealing the capat the through hole 1430.

In a variation of the above process, the solder ball 1420 is placed onthe metallization 1410 of the cap 1400 and bonded thereto to form asolder bump, prior to the through holes 1405 of the cap being aligned tothe stud bumps 1420 provided on a chip 1402.

FIG. 29A illustrates a further embodiment; in which externalinterconnects above the cap 1500 are not soldered to the top surface1502 of the cap. In this case, a sealing material 1505 such as anorganic material which can either be conductive, or nonconductive, e.g.an adhesive material, is applied to the cap 1500 to cover the throughholes 1506 at the top surface 1502. After the cap 1500 is placed overthe chip 1501 and aligned thereto, the cap 1500 and the chip 1501 arepressed together, causing the peaks 1510 of the stud bumps 1516 topenetrate through the sealing material. In yet another alternativeembodiment, the sealing material 1505 can be deposited onto the topsurface 1502 of the cap 1500 after the through holes 1506 have beenaligned to the stud bumps 1516 and then the sealing material is etchedback, leaving the peaks 1510 of the stud bumps substantially free of thesealing material. In still another alternative, the sealing material1502 may be applied around the circumference of the stud bump 1516.Thereafter, further steps are taken to complete the interconnections.For example, a solder ball 1530 can be bonded to the stud bump 1516 toprovide a surface to form a further interconnection, such as to acircuit panel, e.g., such as shown and described above relative to FIGS.8A through 11B. Alternatively, the stud bump can be contacted by asliding or deformable mechanical contact 1540, such as shown in FIG.29B.

FIG. 30 illustrates yet another variation, in which the stud bumps 1516,which may further include a solder or other joining material appliedthereto, are planarized to the top surface 1502 of the cap 1500, afterthe cap 1500 is aligned and joined thereto. The planarized surfaces ofthe stud bumps 1516 thus form a land grid array for interconnection ofthe cap 1500 to further elements such as a circuit panel (not shown).

FIGS. 31 and 32 illustrate yet another alternative embodiment in which acap 1602, is aligned to and placed over a chip 1600 having a stud bumpprovided on bond pad 1604, and thereafter deformed under pressure untilthe stud bump engages the sidewall 1607 of the through hole 1606. Insuch way, the stud bump is ‘coined’ into engagement with the throughhole 1606 in a metal forming operation similar to riveting. In thisembodiment, the cap 1602 need not have a solder-wettable metallizationin the through hole 1606 or on the top surface 1605 of the cap 1602surrounding the through hole. The stud bump is desirably provided of ahighly malleable metal such as gold or alloy thereof, which tends toretain the same shape after being worked in a cold-pressed manner. Whensuch malleable metal is used, the resulting coined stud bump may providea seal of sufficient integrity to the through hole of the cap.Alternatively, an additional fusible material such as solder or tin canthereafter be deposited and reflowed to seal top surface 1605 of the capat the through hole, such as when hermeticity is needed. When the studbump is formed of gold, a fusible material such as solder or tin forms apermanent solid bond.

FIGS. 33-34B illustrate a particular method of simultaneously formingperipheral “picture frame” ring seals between multiple caps of a capelement, e.g., cap wafer, and multiple chips, such as are still attachedin wafer form. In this method, the ring seal is formed by aligning themultiple cap element above a wafer containing the chips and providing aflowable sealing material through an opening in a top surface of the capelement. The sealing material is then allowed or caused to flow downonto the surface of the chips below, at which time the sealing materialthen seals the individual chips to the caps of the cap element.Thereafter, the cap element and the wafer joined thereto are separatedinto individually capped chips by severing chips along dicing lanesbetween each chip.

FIG. 33 is a top-down view illustrating a plurality of chips 1700 eachhaving a device region 1702 provided thereon. Chips having sensitivedevice regions require caps such as those described above in relation toFIGS. 1-3D. Picture frame ring seals 1704 are provided in order to sealthe chips to the caps, preferably when the chips are still in waferform, as one way of protecting against the possibility of degradation tothe devices thereon. A method of simultaneously forming sealssurrounding a device region of the chips will now be described withreference to FIGS. 34A-B.

FIG. 34A is a top-down view and FIG. 34B is a sectional viewillustrating the structure of a cap 1710, such as may be provided aspart of a multiple cap element used in this embodiment. The cap 1710includes ring-like troughs 1712 which are shown overlying a bondinglayer 1714 provided on a front surface of a chip which is disposed belowthe cap 1710. As shown in FIG. 34B, the troughs 1712 extend all the waythrough the cap 1710 from the top surface 1716 to the bottom surface1718 of the cap, and is tapered to become smaller in the direction fromthe top surface towards the bottom surface. A bonding layer 1726, e.g.,a solder-wettable metallization, is provided on sidewalls of the trough1712 as a surface to which a fusible material such as solder wets andfuses to provide a solid bond.

Referring to FIG. 34A, the troughs 1712 extend to almost completelysurround a central portion 1720 of the cap which overlies a deviceregion of the chip, the trough being connected to the central portion1720 by bridges 1722. In a method similar to that described above formaking interconnects with reference to FIGS. 1-3D, a fusible material isprovided in the trough and then caused to flow along the sidewalls ofthe trough down onto the bonding layer 1714 of the chip 1700, as bestseen in FIG. 34B.

In an alternative embodiment, a low-melting point glass or othersuitable material may be placed and flowed downward through the troughto make the seal, in a manner similar to a fusible conductive material.In yet another alternative embodiment, a fluid organic adhesive may beutilized as the sealing material instead of a fusible conductivematerial.

FIG. 35 illustrates a variation of the above-described embodiment inwhich asset of discrete through holes 1812 are provided in caps 1810 ofa cap element 1800, rather than a trough as described above. As showntherein, the cap 1810 is disposed overlying a chip having a centraldevice region 1802, bond pads 1806 and wiring 1806 connecting the deviceregion 1802 to the bond pads 1806, as shown in dotted outline form. Thechip includes a bonding layer 1814 disposed in an annular patternsurrounding the bond pads 1806 and device region 1802 of the chip. Inthis embodiment, the discrete through holes 1812 facilitate the deliveryof a more precisely controlled amount of solder to the bonding layer1814 of the chip, by way of solder balls which are sized to be placed ator within the through holes, in a manner such as described above inrelation to FIG. 3B. To achieve a good ring seal between the chip andthe cap, neither too little solder nor too much solder should beprovided to the bonding layer. Too little solder can cause the sealbetween the chip and the cap to have voids and possible gaps which wouldpermit air or other fluids, e.g., water vapor to reach the device region1802 of the chip. On the other hand, too much solder could cause thesolder to spread beyond the boundaries of the bonding layer to cause ashort circuit.

Accordingly, in this embodiment, solder balls are placed in the throughholes and heated to cause the fusible material to flow laterally alongthe bonding layer 1814 of the chip and a corresponding bonding layer(not shown) of the cap to form a seal which at least substantiallysurrounds the bond pads 1804 and the device region 1802 of the chip. Byjudicious choice of the dimensions of the bonding layer and the size ofthe solder balls, a precisely metered amount of solder can bedistributed to the bonding surfaces. The steps used to form the seal aresimilar to those described above in relation to FIGS. 1-3D or 6A-B forforming electrical interconnects through holes in a chip. Thus, in oneembodiment, the solder balls used to form the ring seal are placed inthe through holes 1812 at or near the time that solder balls used toform the interconnects are placed in the through holes overlying thebond pads 1802, and then all of the solder balls are melted together byone heating operation to form the ring seal at the same time asconductive interconnects are formed.

FIGS. 36A-B illustrate yet another alternative in which fewer throughholes 1912 are provided in caps 1902 of a multiple cap element 1900. Thethrough holes 1912 are also provided at boundaries between respectivechips, thereby greatly decreasing the number of through holes 1912necessary to form the seal of each chip covered by the cap element. Thebonding ring layer 1914 of each chip is provided on the front surfacealong the periphery of the chip 1902 so as to permit the flow of solderfrom within a given through hole 1912 onto the bonding layer 1914 toseal the respective chip, thus forming a structure as shown in thesectional view of FIG. 36B. Note, that as illustrated in FIG. 36B, abonding ring layer 1920 is disposed on the bottom surface 1922 of thecap, as a corresponding wettable metallization onto which the moltensolder spreads during the process of reflowing the solder from thesolder balls to form the seal. The bond pads 1802 and the conductiveinterconnects 1924 joined thereto are desirably formed simultaneouslywith the formation of the ring seal by placing the solder balls in thethrough holes 1912 at or near the same time that solder balls are placedin through holes 1932 used to form the interconnects. Thereafter, asimultaneous heating step can be used to form the electricalinterconnects and the ring seal.

With reference to FIG. 31, a packaged microelectronic device accordingto another embodiment of the invention incorporates a package structureincluding a dielectric interposer 30 having electrically conductivetraces 32 extending along the bottom surface 31 of the dielectricelement. In the embodiment depicted in FIG. 37, the dielectric elementincorporates an aperture or window 36. Terminals in the form ofelectrically conductive posts 38 project downwardly from the bottomsurface 31 of the dielectric element, and are electrically connected totraces 32. A dielectric element with posts thereon can be formed, forexample, by assembling a metallic sheet or plate having projecting poststhereon with a dielectric layer, and etching the sheet or plate to formthe traces. The traces may be disposed on either the bottom surface 31or the top surface 33 of the dielectric element, or within thedielectric element.

A unit 10 as discussed above is assembled with the package structure sothat the top surface 24 of the cover faces upwardly toward the bottomsurface 31 of the interposer 30. The unit connections 18 areelectrically connected to the traces 31, and hence to terminals or posts38. The active area 21 of the chip is aligned with the window 36 in theinterposer. For example, where active area 21 is an optical detector oremitter, the active area can accept or send light through window 36. Inother embodiments, as, for example, where the active area is a MEMSstructure, window 36 may be omitted. The bottom surface 13 of the chipincorporated in unit 10 faces downwardly, and defines a theoreticalhorizontal bottom plane 40 at the level of such bottom surface. Theheight of posts 38 desirably is greater than the thickness or verticalextent of unit 10, so that posts 38 project downwardly beyond bottomplane 40. Thus, the unit connections 18, and hence the electricalconnections to chip 11, are effectively routed to a plane below unit 10.

The package can be mounted on a circuit panel 50 having contact pads 52thereon, as, for example, by soldering the tips of the posts 38 to thecontact pads using conventional surface-mounting soldering techniques.In the completed assembly, unit 10 is positioned with its top surface(the top surface 24 of lid 12) facing upwardly away from circuit panel50. Because the interposer 30 is larger in plan area than the package,this affords the possibility of the metal posts having a diameter andpitch that is suited for attachment of the structure to a PCB (printedcircuit board). Preferably, the interposer 30 or the posts 38 have somedegree of mechanical compliance, so that the structure is able toaccommodate differences in the height of individual pins or nonplanarityof the circuit panel during assembly and/or testing. The mechanicalcompliance desirably accommodates thermal expansion mismatch between thecircuit panel and the unit 10.

A packaged device according to a further embodiment of the invention(FIG. 38) includes a unit 10 as discussed above, together with a packagestructure including a dielectric element having a bottom run 102extending beneath the rear surface 13 of the chip incorporated in theunit and hence extending beneath the bottom plane 40 defined by theunit. The dielectric element further includes a fold region 104projecting upwardly from the bottom run and a top run 106 extending fromthe fold region. The dielectric element preferably is a flexibledielectric film having one or more layers of electrically conductivetraces 105 extending along the film. The traces extend from the bottomrun, along the fold region to the top run. Unit 10 is disposed betweenthe top run 106 and bottom run 102 of the folded dielectric element.Bottom run 102 has terminals 108 connected to traces 105. Terminals 108are exposed through holes 109 at the bottom surface 110 of the bottomrun, which defines the bottom surface of the packaged device. The unitconnections 18 of the unit 10 are bonded to traces 105 on the top run106, and hence are electrically connected to terminals 108. The bondbetween the unit connections and the traces mechanically secures unit 10to the top run. Additional elements such as an adhesive between the topsurface of the unit and top run 106 may be provided for furthersecurement. Alternatively or additionally, the bottom surface of theunit may be secured to the bottom run. An encapsulant (not shown) may beprovided in the space between the runs of the dielectric element, aroundthe unit. Folded package elements for conventional semiconductor chipsare described in U.S. Pat. No. 6,225,688 and in commonly assigned U.S.patent application Ser. No. 10/077,388, filed Feb. 15, 2002; Ser. No.10/640,177, filed Aug. 13, 2003; Ser. No. 60/515,313, filed Oct. 29,2003; and Ser. No. 10/654,375, filed Sep. 3, 2003 the disclosures ofwhich are hereby incorporated by reference herein. Similar structuresand techniques can be used in the folded package for a chip and lidunit. Here again, package terminals 108 may have a different layout inplan than the unit connections 18, and the package terminals may have alarger pitch than the unit connections. The packaged device may besecured to a printed circuit panel as, for example, by solder-bondingthe terminals 108 to the contact pads of the circuit panel. Theterminals 108 may be arranged in a layout which facilitates surfacemounting, with adequate terminal size and pitch. A wide range ofdimensions and pitches may be used to suit any desired application as,for example, to fit a standard pad layout. Furthermore the packagestructure desirably provides mechanical compliance such that it is ableto safely absorb the differential strain mismatch between the circuitpanel and the unit arising from the differential thermal expansionduring manufacture and during service. Here again, the unit can bemounted readily with the top surface 24 of the unit facing upwardly awayfrom the circuit panel. A window 116 optionally may be provided in thetop run 106 of the dielectric element to permit reception of light orother energy through the top run and through the lid of the unit. Asdescribed in the aforementioned incorporated applications, a foldedpackage structure may also define top package terminals (not shown)exposed at the upwardly-facing surface of top run 106. Some or all ofthe top package terminals are connected to some or all of the traces 105and, hence, to some or all of the unit connections 18, to some or all ofthe bottom package terminals 108, or both. The top package terminals canbe used for testing or for attaching a further microelectronic elementas further discussed below, as for example, to stack several packageddevices. The packages of FIG. 37, discussed above, and of FIGS. 39 and40 can also be provided with top package terminals.

The packaged device of FIG. 39 is generally similar to that discussedabove in connection with FIG. 37, except that the package terminals 138exposed at the bottom surface 132 of the interposer 130 are in the formof flat pads rather than downwardly-projecting posts. Thus, theterminals themselves do not project downwardly beyond the bottom plane40 of unit 10. In the embodiment of FIG. 39, additional elements in theform of masses 150 of a bonding material such as, for example,conventional solder balls are provided in contact with the terminals.These additional elements or masses 105 project downwardly beyond thebottom plane. The additional elements or masses 150 can be provided aspart of the packaged device, or may be added during assembly to acircuit panel as, for example, by providing the masses on the contactpads of the circuit panel prior to mounting the packaged device. Theadditional elements or masses desirably have a height or vertical extentgreater than the thickness of unit 10. The additional elements or masses150 desirably provide substantial mechanical compliance. Elements otherthan solder conventional solder spheres may be used. For example,elements commonly referred to as solid-core solder balls, having a coreformed from a high-melting metal such as copper covered by a layer ofsolder may be used. In a further variant, the core of such a ball may behollow or may include a polymeric or other non-metallic material coveredby a thin layer of metal, which in turn may be covered by a solder. Inyet another variant, the additional elements or masses 150 may be massesof a polymer-based conductive material as, for example, a metal-filledsolder. In yet another variant, the additional elements may be providedas pins (not shown) projecting upwardly from the circuit panel or ascontacts on a socket which, in turn, is surface-mounted to the circuitpanel.

The interposer 130 may be rigid, in the case of a direct-bonded copper(DBC) ceramic substrate, semi flexible, for example a PCB, or fullyflexible, as typified by a dielectric film. The choice of material forthe planar interposer will depend on the application. For example, aflexible dielectric film will help absorb thermal expansion mismatchbetween the PCB and the wafer scale package, while a DBC substrate willbe mechanically robust and facilitate the removal of heat from thepackage. The planar interposer is larger in plan area than the unit 10,and hence trace 132 routes unit connections 18 to a layout which isdifferent from, and larger than, the layout of the unit connections.Traces 132 may be provided on either or both sides of interposer 130, orwithin the thickness of the interposer. Where the terminals are disposedabove plane of the interposer bottom surface 132, the terminals areexposed at the bottom surface of the interposer through holes (notshown) extending partially or fully through the interposer. Here again,the interposer may have an aperture in the region of the unit tofacilitate assembly of the structure or provide a passageway forradiation between the unit and the environment.

In the embodiment of FIG. 40, the package structure includes a planarinterposer 230 similar to those used in the embodiments of FIGS. 37 and39, discussed above, and also includes a spacer 202 disposed beneath aperipheral region of the interposer, outside of the area occupied byunit 10. The spacer projects downwardly from the interposer, anddownwardly beyond the bottom plane 40 defined by unit 10. The bottomsurface 204 of the spacer defines a part of the bottom surface of thepackaged device. Spacer 202 is formed from a dielectric material, andhas package terminals 206 disposed on spacer bottom surface 204. Packageterminals 206 are electrically connected by vertical conductors 208carried on spacer 202 to traces 232 on the interposer. Thus, the packageterminals 206 are electrically connected to unit connections 18. Forexample, spacer 202 may include one or more layers of a dielectricmaterial such as a ceramic or polymeric circuit board having throughvias formed therein and partially or completely filled by a conductivematerial forming the vertical conductors 208. In this arrangement, thepackage structure including interposer 230 and spacer 202 defines acavity to accommodate unit 10.

In another arrangement (FIG. 41), the package structure incorporates alead frame having generally ‘S’-shaped leads 302. Leads 302 haveportions 304 overlying the top surface 24 of the unit, these portionsbeing connected to unit connections. 18. The leads 302 also havedownwardly-extending portions 306, and terminal portions 308. Theterminal portions have exposed surfaces 310 forming the packageterminals. These package terminals are disposed below the bottom plane40 of unit 10, and are exposed at the bottom surface of the packagedefined by the bottom surface of the unit. In the embodimentillustrated, the terminal portions project outwardly in horizontaldirections. The downwardly-extending portions 306 also may slopeoutwardly. The package structure optionally may include an overmold orencapsulant 320 surrounding the leads and unit and further securing theleads in place. The overmold or encapsulant 320 should not cover thesurfaces 310 of the terminal portions, so that these surfaces remainexposed for mounting. The overmold may terminate at or above the bottomplane 40 of the unit, or may extend below the unit. In a furthervariant, the downwardly-extending portions 306 of the leads can beattached to the sides of unit 10 as, for example, by a dielectricadhesive, where additional mechanical support is required. In theembodiment depicted in FIG. 41, the lead portions 304 are shown asdirectly connected to unit connections 18 so that these connectionsphysically attach the lead frame to the unit. However, the lead portions304 may be connected to the unit connections by intermediate elementsas, for example, by wire bonds. The techniques commonly employed to joina lead frame with a chip may be used to join the lead frame with unit10.

In the embodiment of FIG. 41, the leads route and fan out the electricalconnections to or below the bottom plane of the unit, provided the leadframe height exceeds the package thickness. The lead frame can be madeto possess a certain degree of compliancy and thereby accommodatethermal expansion mismatch between the wafer scale package and thecircuit panel. Also, it is possible to extend the lead frame in planarea to provide fan out and achieve connection to the circuit panel at acoarser pitch than the interconnects to the wafer scale package.

The embodiment depicted in FIG. 42 is generally similar to theembodiment of FIG. 41, except that the terminal portions 428 of theleads constituting lead frame 422 extend inwardly from thedownwardly-extending portions 426, so that the terminal portions 428,and hence the exposed portions 421 constituting the package terminals,are disposed within the area occupied by unit 10. Thus, the packageddevice as a whole may occupy an area which is approximately the same as,or only slightly larger than, that occupied by unit 10. The leads oflead frame 422 may be resilient, and may be held in place on unit 10 inwhole or in part by resilient engagement with the unit. The unit isresiliently engaged between the terminal portions 428 and the topportions 424 of the leads. Alternatively or additionally, the leads canbe affixed by solder, glass or an organic adhesive on any or all of thefaces of the package that they touch. A similar structure can be madeusing a flexible tape with traces thereon wrapped around the edges ofthe unit. A structure with a flexible tape wrapped around edges of achip is disclosed in certain embodiments of U.S. Pat. No. 5,347,159, thedisclosure of which is incorporated by reference herein. Forapplications where fan-out is required, the metal leads or tape can beprovided with extensions than protrude outside of the plan area of thepackage. In a further variant, an overmold or encapsulant (not shown)may cover the leads and the unit, but desirably does not cover theexposed surfaces 421 of terminal portions 428 of the leads. In a furthervariant, the terminal portions 428, at the innermost extremities 423,may be free of the overmold or encapsulant, to increase flexibility andhence mechanical compliance of the leads. In yet another variant,whether or not an overmold is employed, upwardly facing surfaces 424 onthe upper portions 424 of the leads may remain exposed, so as to provideexposed package terminals at the top of the packaged device as well asat the bottom. As explained further below with reference to FIGS. 50-52,the terminals at the top of the packaged device can be used as testterminals, or for the mounting of additional microelectronic devices. Anadditional microelectronic device mounted on the top package terminalsmay be connected to the unit 10, to the circuit panel upon which thebottom package terminals 428 are mounted, or both by leads 422. Packagesof this type may be mounted in a stacked arrangement, with the topterminals of one device connected to the bottom package terminals of thenext higher device in the stack.

In the structure depicted in FIG. 43, the bottom surface of 13 unit 10(defined by the rear surface of chip 11) is mechanically attached to aplanar interposer 530 by a mounting structure 502 which may include alayer of a die attach material. As discussed above, a wide variety ofmaterials can be used for the interposer. Preferably, the interposer 530is flexible and the mounting structure 502 has appreciable mechanicalcompliance. For example, mounting structure 502 may include a layer of acompliant material. In this embodiment, the bottom surface 531 ofinterposer 530 defines the bottom surface of the packaged device.Terminals 538 are exposed at this bottom surface. Electrical connectionbetween the terminals 538 and the unit connections 18 on the top surfaceof unit 10 are made by leads 506 which may be wire bonds, metallicribbons or the like. The connections between the unit connections 18 andterminals 538 may include other conductive elements such as traces (notshown) extending along the interposer and vias extending through theinterposer. The connections, such as wire bonds 506, desirably areflexible, so that terminals 538 remain movable with respect to unit 10as permitted by the compliance of mounting structure 502. Interposer 530can carry a relatively compact array of terminals 538, at any desiredpitch. Some or all of these terminals may be disposed in the region ofinterposer 530 disposed below unit 10. Arrangements of this type canprovide a high density and space efficient interconnect to the circuitpanel.

As shown in FIGS. 44 and 45, units can be provided with additional unitconnections. In a process according to one embodiment of the invention,a lid element 611 is united with a unitary wafer element 620, such as anentire wafer or a portion of a wafer, incorporating a plurality ofsemiconductor chips 622, so that a bottom surface 612 of the lid elementfaces toward a front surface 624 of the wafer element. A top surface 614of the lid element faces upwardly away from the wafer element. Verticalinterconnect structures 626 are formed so that the vertical interconnectstructures extend upwardly through lid 611 from contacts 628 on the chipso as to provide unit connections exposed at the top surface 614 of thelid element 611. As described in the aforementioned commonly ownedincorporated applications 60/506,600; 60/515,615; 60/532,341; and60/568,041, the lid element may have through vias lined with a thinlayer 630 of a metal. The metallic via liners 630 can be provided, forexample, by depositing the metal on the lid element and selectivelyetching the metal prior to assembly with the wafer element. A solder orother electrically conductive bonding material is provided on the lidelement, on the wafer element or both and reflowed so that the bondingmaterial wets the metal lining in the vias and wets contacts 628 on thewafer element to form the vertical interconnect structures. In theprocess of FIG. 44, the lid element is provided with additional rows ofvias 632 at locations corresponding to the boundaries between chips inthe wafer element. These additional vias may extend partially throughthe lid or entirely through the lid element as depicted in FIG. 44.Additional vias 632 are lined with metal or other conductive material634, and electrically conductive redistribution traces 636 are providedon a surface of the lid so that the traces interconnect the liners insome or all of the additional vias 632 with the via liners 630 in someor all of the other vias used to form the vertical interconnectstructures. The additional liners 634 and traces 636 may be formedduring the same process steps used to make the via liners 630. Thus, theconductive liners 634 in the additional vias will be electricallyconnected to at least some of the vertical interconnect structures 626when the vertical interconnect structures are formed. As described inthe co-pending applications, a sealant 640 is provided between the lidelement and the wafer element at boundaries between adjacent chips, sothat the sealant extends around the periphery of each chip.

After assembly of the lid element, wafer element and sealant, anddesirably after formation of the vertical interconnect structures, thelid element, wafer element and sealant are severed along lines ofseverance 642, also referred to as dicing lanes, one of which is visiblein FIG. 44. The severing step forms individual units, each including oneor more chips and a lid with vertical interconnect elements extendingthrough it. As best seen in the elevational view of FIG. 45, each suchunit has vertically-extensive edge surfaces 649 extending between thetop surface 614 of the lid and the bottom surface 625 of the chip. Thesevering process cuts the additional vias 632, leaving partial viasexposed at the edge surfaces, of the units. As shown in FIG. 45, anelevational view, showing one such edge surface 649, the conductiveliners 634 within the severed vias form edge connections exposed at theedge surfaces of the units. At least some of these edge connections areelectrically connected to at least some of the vertical interconnectstructures 626 and hence to at least some of the contacts 628 on thechip. Edge connections can be provided in this manner on one, some orall of the edge surfaces of the unit. In a variant of this process, theredistribution traces 636 may be formed of the bottom surface 612 of thelid element, rather than on the top surface of such element.

As seen in FIG. 46, the edge connections 634 may be bonded to contactpads 650 of a circuit panel 652 or other substrate so that the unit canbe mounted with the top surface 614 and bottom surface 625 of the unitextending transverse to the plane of the substrate, and with an edgesurface 649 bearing the edge connections facing downwardly toward thesubstrate. Alternatively, the unit can be mounted in a socket 656 (FIG.47) with elements of the socket such as resilient fingers 658 engagingthe edge connections 634 on the edge surfaces 649. The unit also can bemounted as discussed above, with connections made through top unitconnections made by vertical interconnect structures 626.

The embodiment of FIGS. 48A-48B is generally similar to the embodimentdiscussed above with reference to FIGS. 44-47. However, in theembodiment of FIGS. 48 and 49, the sealant 740 extends inwardly from theboundaries of the chips beyond at least some of the verticalinterconnect structures 726. The severance operation is conducted so asto cut through these interconnect structures and thus form thesevertical interconnect structures 726 into edge contacts 734 at edgesurfaces 749. The inwardly-extending sealant 740 remains as a continuousseal between the chip and lid in each unit. The severing operationdepicted in FIG. 48A uses two cuts, along two parallel lines ofseverance, at each boundary between adjacent chips. In a variant, someor all of the contacts 728 and the associated vertical interconnectstructures 726 may lie at the boundary between adjacent chips, so that asingle cut will form a single row of vertical interconnect structuresinto edge contacts on two units. Some or all of the verticalinterconnect structures in each unit may be converted to edge contacts.A unit formed in this manner can be mounted as discussed above withreference to FIGS. 46 and 47. In a further variant (not shown) a unithaving unit connections on the top surface of the lid can be providedwith edge connections by affixing the edge connections onto the unit as,for example, by adhesively bonding a dielectric carrier with conductiveconnections thereon to the edge surfaces of the unit, or by affixingdiscrete edge connection elements to the edge surfaces of the unit. Theaffixed edge connections can be electrically connected to the unitconnections on the top surface of the lid by any suitable connectiontechnique. For example, if the dielectric carrier is a flexibledielectric element with traces thereon, the same can be folded over theedge of the lid so that portions of the traces extend along the lid topsurface to the unit, connections. Alternatively, the edge connectionscan be connected to the unit connections by wire bonding.

A variation of the capped chip structure described above is illustratedin FIGS. 49A-49B. FIG. 49A is a sectional view of the capped chipstructure 730 shown in FIG. 49B through line 49A-49A. In such structure730, the vertical interconnect structures 726, some of which aredisposed along peripheral edges 731 of the chip, are oriented in a firstdirection, as shown in FIG. 49B. Some others of the interconnectstructures are disposed along other peripheral edges 733 of the chip,which are oriented in a second direction which lies at an angle to thefirst direction. For example, the edges 733 are oriented at a rightangle to the edges 731. In a preferred embodiment, some of theinterconnect structures 726 are also disposed at corners 732 between thetwo edges. Providing the interconnect structures along the peripheraledges 731, 733 of the chip, and/or the corners 732 may permit furtherimprovements to reduce the area of the wafer occupied by the chip,because fewer interconnect structures 726 are needed, which consequentlyoccupy less of the chip area. In some cases, the interconnect structures726 are placed as far apart or farther from the device area 204 of thechip, as they are in the embodiments described above with reference toFIGS. 1-3D, for example. This assists in the manufacturability of thestructure and the ability to interconnect the structure 730 in the nexthigher level assembly. Interconnects that are spaced at intervalsfarther apart assist in manufacturability of the higher level assembly,because the tolerances for making such connections of the assembly arenot as tight as they tend to be when fabricating the chip.Interconnection of the structure 730 to the higher level assembly, e.g.,a circuit panel, is preferably by way of mechanical attachment, e.g.,socketing, or electrical connection, such as shown and described abovewith reference to FIGS. 44-47.

A unit 812 (FIG. 50) according to a further embodiment of the inventionincorporates a chip 820 which, like the chips discussed above, has afront face 822 and a rear face 824. Chip 820 has contacts 826 exposed atthe front face 822. Here again, the chip has an active element 827 suchas a microelectromechanical element, an electroacoustic element such asa SAW element, or an optoelectronic element such as an array of sensingpixels, the active element being disposed at or adjacent to the frontface 822. However, in this embodiment, the chip has rear contacts 830exposed at the rear face of the chip. Some or all of the rear-facecontacts 830 are electrically connected to the front-face contacts 826and to the circuit elements of the chip, including the active element827. The electrical connections to the rear-face contacts 830 includeelectrically conductive structures extending partially or completelythrough the thickness of the chip. These conductive structures shouldnot compromise the physical integrity of the unit, and thus should notprovide leakage paths extending between the front and rear surfaces ofthe chip. These connections typically are formed while the chip is beingprocessed as a part of a wafer. One method of forming conductivestructures through the thickness of semiconductor wafers is by ionimplantation, or other techniques, to create a highly doped column 844of semiconductor material in the chip that is sufficiently lowresistivity for the application. Alternatively, a hollow via or “pipe”846 may be carved through the thickness of the semiconductor, so thatthe pipe extends from the rear face 824 to the contact 826 on the frontface. The pipe is sealed at the front surface by the metallic materialof the front-face contact. The walls of the pipe may be made conductiveby coating with a metal film 847. In a variant, the pipe can becompletely filled with metal (not shown).

A wafer element incorporating numerous chips 820 as shown in FIG. 50 isassembled with a lid element including lids 860, one of which is shownin FIG. 50, and with a sealant 862 at the boundaries between adjacentchips in the wafer element, and provided with vertical interconnectstructures 864 extending from at least some of the top face contacts 826on the chip through lid 860 to form top unit connections 866 exposed atthe top surface 868 of the lid. The units are severed from the waferelement, leaving the individual units in the configuration depicted inFIG. 50. In this configuration, the rear face contacts 830 of the chipform bottom unit connections exposed on the bottom surface 824 of thechip, which constitutes the bottom surface of the unit, whereas top unitconnections 866 are exposed at the top surface 868 of the lid, whichconstitutes the top surface of the unit. At least some of the top unitconnections 866 are electrically connected to at least some of thebottom unit connections 830, to the internal circuitry of the chip orboth. The unit provides continuous electrical paths, between at leastsome, and preferably all, of the top unit connections 866 and at leastsome, and preferably all, of the bottom unit connections 830.

The completed unit 812 can be directly mounted on a circuit panel bybonding the bottom unit connections 830 to contact pads on the circuitpanel using techniques similar to those used in flip-chip direct chipmounting. This leaves the unit in a face-up orientation, with the lidand unit top surface 868 facing upwardly away from the circuit panel.Alternatively, the unit 802 can be packaged on an intermediate substrateor interposer 870 (FIG. 51) with the top surface 868 facing away fromthe interposer, and then the interposer be bonded to a circuit panel880. The interposer has package terminals 872 exposed at its bottomsurface, and traces 874 electrically connecting the bottom unitconnections 830 to the terminals. The interposer typically providesredistribution so that the terminals 872 are disposed at a larger pitchthan the bottom terminals 830. The interposer may also providemechanical compliance between the unit and the circuit panel 880. Theinterposer may be generally similar to those used in manufacture ofchip-scale packages.

The top unit connections 866 can be used as test connections to allowengagement of a test probe either before or after mounting the unit to acircuit panel. The top unit connections provide probe pointsadvantageously situated on the top surface of the unit. Moreover, theprobing process will not damage the bottom unit connections that will beconnected to the circuit panel. An additional microelectronic elementmay be connected to the top unit connections 866 to form part of thecircuit in the completed assembly. The additional microelectronicelement may be another unit 812 of similar configuration, so that theunits are stacked vertically as shown in FIG. 52. Top unit connections866 of one unit are connected to the bottom unit connections 830 of thenext higher unit in the stack. The units thus form common verticalbusses disposed inside of the plan area of the units.

In a further embodiment (FIGS. 53-55), bottom unit connections areprovided by forming conductive traces along the edge surfaces of thechip, rather than by providing connections through the chip. As shown inFIG. 53, the wafer element has top surface traces 902 extending from atleast some of the top surface contacts 926 on the chips to theboundaries between chips. A lid element 960 and vertical interconnectstructures 964 forming top unit connections 966 are provided, asdiscussed above. Here again, the wafer element and lid element aresevered by cutting along the boundaries between chips to form individualunits. Thus, after severance, the top surface traces 902 extend to theedge surfaces 904 of the unit. The severing process may be conducted soas to form a trench with sloping edges at the boundaries between units,before severance of the lid element. The sloping trench surfaces providesloping edge surfaces 906 on the chips, as shown in FIG. 54. A furthertrace 910 is formed along this sloping edge surface, typically beforeseverance of the lid element. As shown in FIG. 55, further conductivetraces are formed along the bottom surface 924 of the chip, so as toprovide bottom unit connections 930. Here again, some or all of thebottom unit connections 930 are connected to the circuitry of the chipand to the top unit connections 966. A unit made in this manner can beused as discussed above with reference to FIGS. 50 and 51.

In a further embodiment of the invention (FIG. 56), traces 1002 areprovided on the bottom surface 1061 of the lid element 1060 prior toassembly of the lid element with the wafer element. The traces extendfrom the vias used to form the vertical interconnect structures 1064 tothe areas corresponding to the boundaries between chips. Duringformation of vertical interconnect structures 1064, the solder used toform the vertical interconnect structures makes contact with theinterior ends of traces 1002. After severance of the wafer element 1020and lid element 1060, the ends 1008 of traces 1002 are exposed at theedge surfaces 1049 of the unit. Traces 1010 extending along the edgesurfaces connect traces 1002 with bottom unit contacts 1030 provided onthe bottom surface 1024 of the chip. This arrangement avoids the needfor special processing of the wafer element to form traces 902 asdiscussed above with reference to FIGS. 53-55.

Numerous variations and combinations of the features discussed above canbe used. For example, units having bottom unit connections in additionto top unit, connections can be used with package structures connectedto the top unit, connections as discussed above, for example, thosediscussed with reference to FIGS. 37 and 39. In such an arrangement,both the terminals of the package structure and the bottom unitconnections are exposed at the bottom of the packaged device forconnection to a circuit panel. In a further variant, units can beprovided with both edge unit connections as discussed with reference toFIGS. 44-49 and bottom unit connections as discussed above withreference to FIGS. 50-56.

FIGS. 57-60 illustrate an embodiment of the invention in which anadditional seal is formed to seal peripheral edges of units, i.e.,capped or lidded chips, that are produced by one or the variousembodiments of wafer-scale processes such as described above withreference to FIGS. 1-6B, FIGS. 18-28B, and FIGS. 30-32. FIG. 60illustrates the structure of two such units 2030 that are providedaccording to this embodiment of the invention.

Among many alternatives discussed in the foregoing, an organic materialis a preferred material for use in forming a “picture frame” seal 2002to enclose the active region of a chip, due to the ability of at leastsome such materials to be applied and form bonds at an ambienttemperature to only slightly elevated temperatures. Use of suchmaterials helps to avoid the above-described CTE mismatch problems,particularly when the chip-containing wafer and the lid-containing waferare of different materials. The use of such organic sealing material isparticularly advantageous in conjunction with the low-temperatureprocesses described above for forming interconnects, such as those inwhich stud bumps are mounted to the chips which remain in wafer form,and a lid or cap-containing wafer is then aligned and sealed with aconductive or nonconductive organic material to form interconnects(e.g., as shown and described above relative to FIGS. 29A and 30).Certain types of chips, particularly those containing SAW devices, areespecially sensitive to strain. SAW devices typically operate to providea narrow bandpass filter function in which the center frequency of thepassband is subject to change due to a strain in the device. The lowmodulus of elasticity of organic materials helps the organic material tomitigate the effects of differential strain which occurs between thechip-containing wafer and the lid wafer due to CTE mismatch.

However, despite the foregoing benefits, an organic material may notprovide a sufficiently hermetic seal for some devices. A tighter seal isgenerally achieved through inorganic materials such as a metal or glassrather than organic materials, but is subject to the above-describeddifficulties.

Hence, in the embodiment illustrated in FIG. 60, an additional layer2004 is deposited and patterned to overlie peripheral edges 2020 of theunit, as an impermeable medium to seal edges 2006 of the chip 2001, theedges 2008 of the lid, as well as the organic seal material 2002. Asalso shown in FIG. 60, the same layer 2004, when provided of aconductive material, is also desirably patterned to form metal contacts2010 connected to respective ones of the conductive interconnects 2012on each chip 2001.

FIGS. 57-59 show stages in an illustrative method of fabricating theunits 2030 shown in FIG. 60. As shown in FIG. 57, a pair of units 2030are shown, each remaining attached at boundary 2034 as portions of awafer. For ease of reference, only two such units are shown. However, asubstantial number of such units can be simultaneously processed inwafer form according to the method described herein. Each chip includesa device 2011, e.g., illustratively, a SAW or MEMs device, a void 2013disposed above the device and conductive interconnects 2012 extendingupwardly from the chips 2001.

A photosensitive resist film is patterned by photolithography to formresist patterns 2032 on the surface 2022 of the lid portion of theunits. Illustratively, the resist film is a lift-off film, in that anymaterial coating applied onto the resist film will also be removed whenthe resist film is subsequently removed. The resist patterns 2032 areformed as islands surrounding each of the pre-existing interconnects2012, so as to maintain the interconnects isolated from each other uponthe subsequent removal of the resist patterns with metal coating appliedthereto.

Thereafter, as shown in FIG. 58, the individual units 2030 are partiallysevered along boundary 2034, which preferably coincides with the dicinglane of the chips, to produce the structure shown. In a further stepillustrated in FIG. 59, one or more metals is deposited to produce thestructure shown in which both the peripheral edges 2020 and the topsurfaces 2022 of the units are covered by metal. The metal is preferablychosen for its qualities in functioning as a barrier to contaminantsincluding moisture, and its ability to conduct electricity. Metals whichdo not corrode easily are preferred for this purpose. The metal layer2004 should preferably be selected so as to form a coating which adheresstrongly to the surfaces of the unit, as well as adhering to the sealingmaterial 2002 and to provide good conductivity in both a directionacross the major surface of the layer and the direction through itsthickness. For these reasons, the metal layer 2004 is preferably formedof a stack of deposited metals, such as are used in the semiconductorand MEMs fabrication industries. Common examples of metals which may beused to form such stacks include combinations of titanium, platinum andgold, as well as combinations of chromium, copper and gold, combinationsof zinc, nickel and palladium, as well as various permutations andcombinations of the above-listed metals. Nickel can be included in themetal layer stack to increase the ability of the patterned metal toprovide magnetic screening. The thickness of each patterned metal layerof the stack is illustratively on the order of about 0.1 μm when themetal layer is applied by vapor phase deposition and up to about 1 μmwhen the metal layer is applied by aqueous processing. A conductivenon-metal, for example, a conductive nitride such as titanium nitride orother nitride of a metal, can be utilized as a portion or all of acoating in place of a metal, provided that the material provides arequisite barrier function to moisture or contamination and hassufficient conductivity.

Thereafter, referring again to FIG. 60, steps are performed to removethe resist patterns 2032 together with the unwanted portions of themetal layer, to produce the structure shown as described above. Theunits 2030 are also severed at this time into individual units alongdicing lanes at the boundary 2034 (FIG. 58).

In addition to the foregoing described embodiment shown in FIG. 60, theabove-described process can be modified to provide several alternativestructures. FIG. 61 illustrates one such alternative structure. As showntherein, an electrical connection can be established between respectiveones of the interconnects 2012 and a peripheral metal sealing layer2004, to maintain the sealing layer and one interconnect of the chip atthe same potential, such as to provide a ground contact. Other ones 2014of the interconnects can connect to contacts 2010 patterned from themetal layer as described above. In such embodiment, the peripheral metalsealing layer 2004 preferably extends over most of the exteriorperipheral 2020 and top surfaces 2022 of the unit 2030. In such case,the sealing layer 2004 can be used to provide an electromagneticshielding function for the unit 2030.

With continued reference to FIG. 61, in a variation of the aboveembodiment, the metal layer 2004 is patterned to provide conductivetraces which extend laterally over the top surface 2022 of the lid. Suchconductive trace can be used for redistribution of contacts, e.g., in amanner similar to that described above with reference to FIGS. 4A-B and7B, to convert, for example, between the pitch and lateral dimensions ofthe interconnects 2012 of the unit and those of an industry standardland grid array.

In a particular embodiment, the patterned metal layer 2004 can be usedfor additional functions, such as the provision of conductive elementson the surface 2022 of the unit for use as resistive, inductive orcapacitive devices, e.g., for the purpose of providing impedancematching between the device of the chip 2001 and an external network towhich the unit is attached in later assembly steps. To form certain onesof such conductive elements, prior to the final step of severing thechips, a dielectric layer can be deposited and patterned to overlie thepatterned metal layer 2004, followed by the deposition and patterning ofone or more additional patterned metal layers, as described above withreference to FIGS. 57-59.

As these and other variations and combinations of the features discussedabove can be utilized without departing from the present invention asdefined by the claims, the foregoing description of the preferredembodiments should be taken by way of illustration rather than by way oflimitation of the invention as defined by the claims.

1. A capped chip, comprising: a chip having a front surface, one or moredevices at said front surface, and a first annular solder-wettablemetallization enclosing said one or more devices; a cap member having atop surface, a bottom surface opposite said top surface, one or morethrough holes extending between said top and bottom surfaces and asecond annular solder-wettable metallization at said bottom surface inregistration with said one or more through holes and said first annularsolder-wettable metallization; and a sealing medium including a fusiblematerial bonded to said first and second solder-wettable metallizations.2. The capped chip as claimed in claim 1, wherein said sealing mediumincludes at least one material selected from the group consisting ofsolder, eutectic composition, and tin.
 3. The capped chip as claimed inclaim 2, wherein said one or more through holes is sized to permit aflow of said sealing medium from said one or more through holes ontosaid first and second annular solder-wettable metallizations.
 4. Thecapped chip as claimed in claim 3, wherein said one or more throughholes is tapered to become smaller in a direction from said top surfaceof said cap member towards said bottom surface.
 5. The capped chip asclaimed in claim 3, wherein said chip further includes a plurality ofbond pads exposed at said front surface enclosed by said first annularsolder-wettable metallization, and a plurality of metallic interconnectsextending from said bond pads at least partially through said capmember.